LIBRARY 


UNIVERSITY  OF  CALIFORNIA. 


OF" 


r 


A   COURSE 


OF 


ELEMENTARY     INSTRUCTION 


IN 


PRACTICAL  BIOLOGY. 


A  COURSE 

or 

PRACTICAL  INSTRUCTION 


IN 


ELEMENTARY    BIOLOGY 


BY 


T.  H.  HUXLEY,  LL.D.,  SEC.  R.S., 


ASSISTED   BY 


H.  N.  MARTIN,  B.A.,  M.B.,  D.Sc., 

PROFESSOR   OF   BIOLOGY   IN   JOHNS  HOPKINS  UNIVERSITY,  BALTIMORE; 

FELLOW  OF  CHRIST'S  COLLEGE,  CAMBRIDGE,  AND  OF 
UNIVERSITY  COLLEGE,  LONDON. 


,    THIRD  EDITION,  REVISED. 
*" 

THE 

NIVERSITY 


MACMILLAN    AND    CO 
1877. 


BIOLOGY 

LIBRARY 

G 


COPYRIGHT,  1877, 

BY 
H.  NEWELL  MARTIN. 


PREFACE. 


VERY  soon  after  I  began  to  teach  Natural  History,  or  what 
we  now  call  Biology,  at  the  Royal  School  of  Mines,  some 
twenty  years  ago,  I  arrived  at  the  conviction  that  the  study 
of  living  bodies  is  really  one  discipline,  which  is  divided  into 
Zoology  and  Botany  simply  as  a  matter  of  convenience;  and 
that  the  scientific  Zoologist  should  no  more  be  ignorant  of 
the  fundamental  phenomena  of  vegetable  life,  than  the  scien- 
tific Botanist  of  those  of  animal  existence. 

Moreover,  it  was  obvious  that  the  road  to  a  sound  and 
thorough  knowledge  of  Zoology  and  Botany  lay  through 
Morphology  and  Physiology;  and  that,  as  in  the  case  of  all 
other  physical  sciences,  so  in  these,  sound  and  thorough 
knowledge  was  only  to  be  obtained  by  practical  work  in 
the  laboratory. 

M.  * 


vi  PREFACE. 

The  thing  to  be  done,  therefore,  was  to  organize  a  course 
of  practical  instruction  in  Elementary  Biology,  as  a  first 
step  towards  the  special  work  of  the  Zoologist  and  Botanist. 
But  this  was  forbidden,  so  far  as  I  was  concerned,  by  the 
limitations  of  space  in  the  building  in  Jermyn  Street,  which 
possessed  no  room  applicable  to  the  purpose  of  a  labora- 
tory ;  and  I  was  obliged  to  content  myself,  for  many  years, 
with  what  seemed  the  next  best  thing,  namely,  as  full  an 
exposition  as  I  could  give  of  the  characters  of  certain  plants 
and  animals,  selected  as  types  of  vegetable  and  animal  or- 
ganization, by  way  of  introduction  to  systematic  Zoology 
and  Palaeontology. 

In  1870,  my  friend  Professor  Rolleston,  of  Oxford,  pub- 
lished his  "  Forms  of  Animal  Life"  It  appears  to  me  that  this 
exact  and  thorough  book,  in  conjunction  with  the  splendid 
appliances  of  the  University  Museum,  leaves  the  Oxford 
student  of  the  fundamental  facts  of  Zoology  little  to  desire. 
But  the  Linacre  Professor  wrote  for  the  student  of  Animal 
life  only,  and,  naturally,  with  an  especial  eye  to  the  condi- 
tions which  obtain  in  his  own  University ;  so  that  there  was 
still  room  left  for  a  Manual  of  wider  scope,  for  the  use  of 
learners  less  happily  situated. 

In  1872  I  was,  for  the  first  time,  enabled  to  carry  my  own 
notions  on  this  subject  into  practice,  in  the  excellent  rooms 
provided  for  biological  instruction  in  the  New  Buildings  at 
South  Kensington.  In  the  short  course  of  Lectures  given 


PREFACE.  vii 

to  Science  Teachers  on  this  occasion,  I  had  the  great  ad- 
vantage of  being  aided  by  my  friends  Dr  Foster,  F.R.S., 
Prof.  Rutherford,  F.R.S.,  and  Prof.  Lankester,  F.  R.  S.,  whose 
assistance  in  getting  the  laboratory  work  into  practical  shape 
was  invaluable. 

Since  that  time,  the  biological  teaching  of  the  Royal 
School  of  Mines  having  been  transferred  to  South  Kensing- 
ton, I  have  been  enabled  to  model  my  ordinary  course  of 
instruction  upon  substantially  the  same  plan. 

The  object  of  the  present  book  is  to  serve  as  a  laboratory 
guide  to  those  who  are  inclined  to  follow  upon  the  same 
road.  A  number  of  common  and  readily  obtainable  plants 
and  animals  have  been  selected  in  such  a  manner  as  to 
exemplify  the  leading  modifications  of  structure  which  are 
met  with  in  the  vegetable  and  animal  worlds.  A  brief  de- 
scription of  each  is  given ;  and  the  description  is  followed 
by  such  detailed  instructions  as,  it  is  hoped,  will  enable  the 
student  to  know,  of  his  own  knowledge,  the  chief  facts 
mentioned  in  the  account  of  the  animal  or  plant.  The 
terms  used  in  Biology  will  thus  be  represented  by  clear  and 
definite  images  of  the  things  to  which  they  apply;  a  com- 
prehensive, and  yet  not  vague,  conception  of  the  phenomena 
of  Life  will  be  obtained ;  and  a  firm  foundation  upon  which 
to  build  up  special  knowledge  will  be  laid. 

The  chief  labour  in  drawing  up  these  instructions  has 
fallen  upon  Dr  Martin.  For  the  general  plan  used,  and  the 


viii  PREFACE. 

descriptions  of  the  several  plants  and  animals,  I  am  respon- 
sible j  but  I  am  indebted  for  many  valuable  suggestions  and 
criticisms  from  the  botanical  side  to  my  friend  Prof.  Thisel- 
ton  Dyer. 


T.  H.  H. 


LONDON, 

September,   1875. 


CONTENTS. 


I. 

YEAST. 

General  characters — Fermentation — Appearances  of  yeast  under  the 
microscope — Structure  of  yeast  cells — Chemical  composition — Mode  of 
multiplication — Growth  in  Pasteur's  fluid— Physiology  of  yeast — La- 
boratory work.  .  .  .  ...  .  .  • .';  :.-,-  >;.  p.  i — 10. 

II. 
PROTOCOCCUS. 

Habitat — Histological  structure — Modes  of  multiplication — Depend- 
ence on  light — Physiology  of  Protococcus — Motile  stage — Laboratory 
work.  "/''*-;"/.  '-•"'•'..  .  .'  '.  '  .  p.  n — 16. 

III. 

PROTEUS  ANIMALCULE.    COLOURLESS  BLOOD  CORPUSCLES. 

AMOEBA — Habitat — Movements — Structure — Chemical  composition 
—Effects  of  temperature  and  electric  shocks — Encystation — COLOUR- 
LESS BLOOD  CORPUSCLES — Movements— Structure— The  influence  of 
various  reagents  on  them — Physiology  of  Amoeba.  Laboratory  work. 

p.  17—24. 

IV. 

BACTERIA. 

Form  and  structure — Movements— Spirillum  volutans — Stationary 
stage— Zoogloea — Growth  in  Pasteur's  fluid— Relation  to  putrefaction — 
Power  of  resisting  desiccation — Laboratory  work.  .  .  p.  25 — 29. 


x  CONTENTS. 

V. 

MOULDS. 

Fungi — Their  spores — PENICILLIUM — Habitat — General  characters 
— Form  and  structure — Development — MUCOR— Habitat — Form  and 
structure — Development,  asexual  and  sexual — Alternation  of  generations 
— Mucor  Torula — Laboratory  work.  .  .  .  .  p.  30 — 41. 

VI. 

STONEWORTS. 

Habitat  and  general  characters— Development— Mode  of  growth  and 
microscopic,  structure — Protoplasmic  movements — Organs  of  reproduc- 
tion— Physiology— Laboratory  work.  .  ......  .  p.  42—54. 

VII. 

THE  BRACKEN  FERN. 

Habit — Structure,  gross  and  microscopic— The  various  tissues — 
Mode  of  growth — Development — Prothallus — Sexual  organs — Alterna- 
tion of  generations — Laboratory  work p.  55 — 69. 

VIII. 
THE  BEAN  PLANT. 

Habit — General  Structure — Development  and  mode  of  growth — 
Sexual  organs — Homology  with  the  reproductive  organs  of  the  Fern — 
Physiology — Laboratory  work.  .  »  .  .  .  .  p.  70 — 88. 

IX. 
THE  BELL  ANIMALCULE. 

Habit  and  distribution— Anatomy — Movements — Contractile  vesicle 
— Ingestion — Modes  of  multiplication — Encystation — Laboratory  work. 

p.  89—97. 


CONTENTS.  xi 

X. 

FRESH-WATER  POLYPES. 

Habit  and  form — Naked-eye  appearances — Mode  of  feeding — Mul- 
tiplication— Microscopic  structure — Relationships  to  simpler  plants  and 
animals — Laboratory  work.  ".*•'.  .  ».  .  p.  98 — 106. 

XL 

THE  FRESH-WATER  MUSSEL. 

General  structure — Respiratory  organs — Alimentary  organs — Circu- 
latory system — Excretory  organs — Reproductive  organs — Development 
— Laboratory  work.  . p.  re  7  — 126. 

XII. 
THE  FRESH-WATER  CRAYFISH  AND  THE  LOBSTER. 

Habitat — General  structure—  Appendages — Segments — Alimentary 
canal — Circulatory  organs — Respiratory  organs — The  green  glands — 
Nervous  system — Sense  organs — Reproductive  organs — Development — 
Laboratory  work.  .  r;.  -  .  ....  p.  127 — 158. 

XIII. 
THE  FROG. 

General  characters — Development — Specific  characters  of  Rana  tern- 
poraria  and  R.  esculenta — The  pleuroperitoneal  cavity  and  the  alimen- 
tary canal — The  neural  canal  and  the  cerebro-spinal  axis — Objects  seen 
on  transverse  sections  at  various  points — Comparison  with  lobster — The 
skeleton — The  digestive  system — The  blood  and  lymph  vascular  systems 
— The  ductless  glands — The  respiratory  organs — The  urinary  organs — 
The  generative  organs — The  nervous  system — The  sense  organs — La- 
boratory work.  .  .  .  .  «  .  .  .  p.  rsp — 267. 

APPENDIX p.  268. 


YEAST  (Torula  or  Saccharomyces  Cerevisice). 

YEAST  is  a  substance  which  has  been  long  known  on  ac- 
count of  the  power  which  it  possesses  of  exciting  the  process 
termed  fermentation  in  substances  which  contain  sugar. 

If  strained  through  a  coarse  filter,  it  appears  to  the  naked 
eye  as  a  brownish  fluid  in  which  no  solid  particles  can  be 
discerned.  When  some  of  this  fluid  is  added  to  a  solution 
of  sugar  and  kept  warm,  the  mixture  soon  begins  to  dis- 
engage bubbles  of  gas  and  become  frothy ;  its  sweetness 
gradually  disappears ;  it  acquires  a  spirituous  flavour  and 
intoxicating  qualities ;  and  it  yields  by  distillation  a  light 
fluid — alcohol  (or  spirits  of  wine)  which  readily  burns. 

When  dried  slowly  and  at  a  low  temperature,  yeast  is 
reduced  to  a  powdery  mass,  which  retains  its  power  of 
exciting  fermentation  in  a  saccharine  fluid  for  a  considerable 
period.  If  yeast  is  heated  to  the  temperature  of  boiling 
water,  before  it  is  added  to  the  saccharine  fluid,  no  ferment- 
ation takes  place ;  and  fermentation  which  has  commenced 
is  stopped  by  boiling  the  saccharine  liquid. 

A  saccharine  solution  will  not  ferment  spontaneously.  If 
it  begins  to  ferment,  yeast  has  undoubtedly  got  into  it  in 
some  way  or  other. 

If  the  yeast  is  not  added  directly  to  the  saccharine  fluid, 
but  is  separated  from  it  by  a  very  fine  filter,  such  as  porous 
earthenware,  the  saccharine  fluid  will  not  ferment,  although 
the  filter  allows  the  fluid  part  of  the  yeast  to  pass  through 
into  the  solution  of  sugar. 


2  ELEMENTARY  BIOLOGY.  [CHAP. 

If  the  saccharine  fluid  is  boiled,  so  as  to  destroy  the 
efficiency  of  any  yeast  it  may  accidentally  contain,  and  then 
allowed  to  come  in  contact  only  with  such  air  as  has  been 
passed  through  cotton  wool,  it  will  never  ferment.  But  if 
it  is  exposed  freely  to  the  air,  it  is  almost  sure  to  ferment 
sooner  or  later,  and  the  probability  of  its  so  doing  is  greatly 
increased  if  there  is  yeast  anywhere  in  the  vicinity. 

These  experiments  afford  evidence  (!)  that  there  is  some- 
thing in  yeast  which  provokes  fermentation,  (2)  that  this 
something  may  have  its  efficiency  destroyed  by  a  high  tem- 
perature, (3)  that  this  something  consists  of  particles  which 
may  be  separated  from  the  fluid  which  contains  them  by  a 
fine  filter,  (4)  that  these  particles  may  be  contained  in  the 
air;  and  that  they  may  be  strained  off  from  the  air  by 
causing  it  to  pass  through  cotton  wool. 

Microscopic  examination  of  a  drop  of  yeast  shews  what 
the  particles  in  question  are. 

Even  with  a  hand-glass,  the  drop  no  longer  appears 
homogeneous,  as  it  does  to  the  naked  eye,  but  looks  as  if 
fine  grains  of  sand  were  scattered  through  it ;  but  a  con- 
siderable magnifying  power  (5 — 6co  diameters)  is  necessary 
to  shew  the  form  and  structure  of  the  little  granules  which 
are  thus  made  visible.  Under  this  power,  each  granule 
(which  is  termed  a  Toruld)  is  seen  to  be  a  round,  or  oval, 
transparent  body,  varying  in  diameter  from  o-jV^th  to 
•y^j-th  of  an  inch  (on  the  average  about  g^pth). 

The  Torulcs  are  either  single,  or  associated  in  heaps  or 
strings.  Each  consists  of  a  thin-walled  sac,  or  bag,  contain- 
ing a  semi-fluid  matter,  in  the  centre  of  which  there  is  often 
a  space  full  of  a  more  clear  and  watery  fluid  than  the  rest, 
which  is  termed  a  'vacuole.'  The  sac  is  comparatively 
tough,  but  it  may  be  easily  burst,  when  it  gives  exit  to  its 
contents,  which  readily  diffuse  themselves  through  the  sur- 


I.]  YEAST.  3 

rounding  fluid.  The  whole  structure  is  called  a  'cell;'  the 
sac  being  the  '  cell-wall '  and  the  contents  the  '  protoplasm.' 

When  yeast  is  dried  and  burned  in  the  open  air  it  gives 
rise  to  the  same  kind  of  smell  as  burning  animal  matter, 
and  a  certain  quantity  of  mineral  ash  is  left  behind.  Ana- 
lysed into  its  chemical  elements,  yeast  is  found  to  contain 
Carbon,  Hydrogen,  Oxygen,  Nitrogen,  Sulphur,  Phosphorus, 
Potassium,  Magnesium  and  Calcium;  the  last  four  in  very 
small  quantities. 

These  elements  are  combined  in  different  ways,  so  as  to 
form  the  chief  proximate  constituents  of  the  Torulat  which 
are  (i)  a  Protein  compound,  analogous  to  Casein,  (2)  Cellu- 
lose, (3)  Fat,  and  (4)  Water.  The  cell-wall  contains  all  the 
Cellulose  and  a  small  proportion  of  the  mineral  matters. 
The  protoplasm  contains  the  Protein  compound  and  the  Fat 
with  the  larger  proportion  of  the  mineral  salts. 

These  Torulcs,  are  the  '  particles '  in  the  yeast  which  have 
the  power  of  provoking  fermentation  in  sugar ;  it  is  they 
which  are  filtered  off  from  the  yeast  when  it  loses  its  effi- 
ciency by  being  strained  through  porous  earthenware;  it 
is  they  which  form  the  fine  powder  to  which  yeast  is  reduced 
by  drying,  and  which,  from  their  extreme  minuteness,  are 
readily  diffused  through  the  air  in  the  form  of  invisible 
dust. 

That  the  Torulce  are  living  bodies  is  proved  by  the  manner 
in  which  they  grow  and  multiply.  If  a  small  quantity  of 
yeast  is  added  to  a  large  quantity  of  clear  saccharine  fluid 
so  as  hardly  to  disturb  its  transparency,  and  the  whole  is 
kept  in  a  warm  place,  it  will  gradually  become  more  and 
more  turbid,  and,  after  a  time,  a  scum  of  yeast  will  collect, 
which  may  be  many  thousand,  or  million,  times  greater  in 
weight  than  that-which  was  originally  added.  If  the  Torulce 
are  examined  as  this  process  of  multiplication  is  going  on,  it 

I 2 


4  ELEMENTARY  BIOLOGY.  [CHAP. 

will  be  found  that  they  are  giving  rise  to  minute  buds,  which 
rapidly  grow,  assume  the  size  of  the  parent  Torula^  and 
eventually  become  detached ;  though,  generally,  not  until 
they  have  developed  other  buds,  and  these  yet  others.  The 
Torulcc  thus  produced  by  gemmation,  one  from  the  other, 
are  apt  long  to  adhere  together,  and  thus  the  heaps  and 
strings  mentioned,  as  ordinarily  occurring  in  yeast,  are  pro- 
duced. No  Torula  arises  except  as  the  progeny  of  another; 
but,  under  certain  circumstances,  multiplication  may  take 
place  in  another  way.  The  Torula  does  not  throw  out  a  bud, 
but  its  protoplasm  divides  into  (usually)  four  masses,  termed 
ascospores,  each  of  which  surrounds  itself  with  a  cell-wall, 
and  the  whole  are  set  free  by  the  dissolution  of  the  cell- 
wall  of  the  parent.  This  is  multiplication  by  endogenous 
division. 

As  each  of  the  many  millions  of  Torulcz  which  may  thus 
be  produced  from  one  Torula  has  the  same  composition  as 
the  original  progenitor,  it  follows  that  a  quantity  of  Protein, 
Cellulose  and  Fat  proportional  to  the  number  of  Torula 
thus  generated,  must  have  been  produced  in  the  course  of 
the  operation.  Now  these  products  have  been  manufactured 
by  the  Torulce  out  of  the  substances  contained  in  the  fluid 
in  which  they  float  and  which  constitute  their  food. 

To  prove  this  it  is  necessary  that  this  fluid  should  have 
a  definite  composition.  Several  fluids  will  answer  the  pur- 
pose, but  one  of  the  simplest  (Pasteur's  solution)  is  the 
following. 

Water (H2O). 

Sugar (C]9HMOn). 

Ammonium  Tartrate     (C4H4(NH4)aO6). 

Potassium  Phosphate    (KH2PO4). 

Calcium  Phosphate       (Ca3P2O8). 

Magnesium  Sulphate     (MgSOJ. 


I.]  YEAST.  5 

In  this  fluid  the  Torula  will  grow  and  multiply.  But  it 
will  be  observed  that  the  fluid  contains  neither  Protein  nor 
Cellulose,  nor  Fat,  though  it  does  contain  the  elements  of 
these  bodies  arranged  in  a  different  manner.  It  follows  that 
the  Torula  must  absorb  the  various  substances  contained  in 
the  water  and  arrange  their  elements  anew,  building  them 
up  into  the  complex  molecules  of  its  own  body.  This  is  a 
property  peculiar  to  living  things. 

The  Torula  being  alive,  the  question  arises  whether  it  is 
an  animal  or  a  plant.  Although  no  sharp  line  of  demarca- 
tion can  be  drawn  between  the  lowest  form  of  animal  and  of 
vegetable  life,  yet  Torula  is  an  indubitable  plant,  for  two 
reasons.  In  the  first  place,  its  protoplasm  is  invested  by 
a  continuous  cellulose  coat,  and  thus  has  the  distinctive 
character  of  a  vegetable  cell.  Secondly,  it  possesses  the 
power  of  constructing  Protein  out  of  such  a  compound  as 
Ammonium  Tartrate,  and  this  power  of  manufacturing 
Protein  is  distinctively  a  vegetable  peculiarity.  Torula 
then  is  a  plant,  but  it  contains  neither  starch  nor  chlorophyll, 
it  absorbs  oxygen  and  gives  off  carbonic  anhydride,  thus 
differing  widely  from  the  green  plants.  On  the  other  hand, 
it  is,  in  these  respects,  at  one  with  the  great  group  of  Fungi. 
Like  many  of  the  latter,  its  life  is  wholly  independent  of 
light,  and  in  this  respect,  again,  it  differs  from  the  green 
plants. 

Whether  Torula  is  connected  with  any  other  form  of 
Fungi  is  a  question  which  must  be  left  open  for  the  present. 
It  is  sufficient  to  mention  the  fact  that  under  certain  circum-' 
stances  some  Fungi  (e.  g.  Mucor)  may  give  rise  to  a  kind  of 
Torula  different  from  common  yeast. 

The  fermentation  of  the  sugar  is  in  some  way  connected 
with  the  living  condition  of  the  Torula,  and  is  arrested  by  all 
those  conditions  which  destroy  the  life  of  the  I'orula  and 


6  ELEMENTARY  BIOLOGY.  [CHAP. 

prevent  its  growth  and  reproduction.  The  greater  part  of 
the  sugar  is  resolved  into  Carbonic  anhydride  and  Alcohol, 
the  elements  of  which,  taken  together,  equal  in  weight  those 
of  the  sugar.  A  small  part  breaks  up  into  Glycerine  and 
Succinic  acid,  and  one  or  two  per  cent,  is  not  yet  accounted 
for,  but  is  perhaps  assimilated  by  the  Torulce. 

This  is  the  more  probable  as  Torulcz  will  grow  and  multiply 
actively  in  a  solution  in  which  sugar  and  Ammonium  Nitrate 
replace  the  Ammonium  Tartrate  of  the  former  solution,  in 
which  case  the  carbon  of  the  Protein,  Cellulose  and  Fat 
manufactured,  must  be  obtained  from  the  sugar.  Moreover, 
though  oxygen  is  essential  to  the  life  of  the  Torula,  it  can 
live  in  saccharine  solutions  which  contain  no  free  oxygen, 
appearing,  under  these  circumstances,  to  get  its  oxygen  from 
the  sugar. 

It  has  further  been  ascertained  that  Torulcz  flourish  re- 
markably in  solutions  in  which  sugar  and  pepsin  replace 
the  Ammonium  Tartrate.  In  this  case,  the  nitrogen  of  their 
protein  compounds  must  be  derived  from  the  pepsin ;  and 
it  would  seem  that  the  mode  of  nutrition  of  such  Torula 
approaches  that  of  animals. 

LABORATORY  WORK. 

Sow  some  fresh  baker's  yeast  in  Pasteur's  fluid1   with 

1   Pasteur's  fluid : 

Potassium  Phosph 20  parts. 

Calcium  Phosph 2      ,, 

Magnesium  Sulphate c      ,, 

Ammonium  Tartrate 100      ,, 

[Cane  Sugar  1500      „] 

Water 8576      „ 

10,000  parts. 

The  sugar  is  to  be  omitted  when  Pasteur's  fluid  "without  sugar"  is 
ordered.  Pasteur  himself  used  actual  yeast  ash ;  the  above  constituents 
give  an  imitation  ash,  which,  with  the  ammonium  salt  and  sugar, 
answers  all  practical  purposes. 


I.]  YEAST.  7 

sugar  and  keep  it  in  a  warm  place  :  as  soon  as  the  mixture 
begins  to  froth  up,  and  the  yeast  is  manifestly  increasing  in 
quantity,  it  is  icady  for  examination. 

A.     MORPHOLOGY. 

1.  Spread  a  little  out,  on  a  slide,  in  a  drop  of  the  fluid, 
and  examine  it  with  a  low  power  (J  inch  objective, 
Hartnack,  No.  4)  without  a  cover-glass.     Note  the 
varying  size  of  the  cells,  and  their  union  into  groups. 

2.  Cover  a  similar  specimen   with  a   thin   glass  and 
examine  it  under  a  high  power  (J  objective.     Hart- 
nack, No.  7  or  8,  Oc.  3  or  4). 

a.  Note  the  size  (measure),  shape,  surface  and  mode 
of  union  of  the  cells. 

b.  Their  structure  :  sac,  protoplasm,  vacuole. 
a.      Sac;  homogeneous,  transparent. 

ft.     Protoplasm;  less  transparent;  often  with  a  few 

clear  shining  dots  in  it. 

y.       Vacuole ;  sometimes  absent ;  size,  position. 
S.      The  relative  proportion  of  sac,  protoplasm,  and 

vacuole  in  various  cells. 
Draw  a  few  cells  carefully  to  scale. 

3.  Run  in  magenta  solution  under  the  cover-glass.    (This 
is  readily  done  by  placing  a  drop  of  magenta  so- 
lution in  contact  with  one  side  of  the  cover-glass, 
and  a  small  strip  of  blotting  paper  at  the  opposite 
side.) 

a.  Note  what  cells  stain  soonest  and  most  deeply, 
and  what  part  of  each  cell  it  is  that  stains  :  the  sac 
is  unaffected ;  the  protoplasm  stained ;  the  vacuole 
unstained,  though  it  frequently  appears  pinkish, 
being  seen  through  a  coloured  layer  of  protoplasm. 


8  ELEMENTARY  BIOLOGY.  [CHAP. 

4.  Burst  the  stained  cells  by  placing  a  few  folds   of 
blotting  paper  on  the  surface  of  the  cover-glass  and 
pressing   smartly   with   the    handle    of  a  mounted 
needle:  note  the   torn   empty  and  colourless,  but 
solid    and    uncrushed    transparent   sacs ;    the    soft 
crushed  stained  protoplasm. 

5.  Repeat  observation  3,  running   in  iodine   solution 
instead  of  magenta.     The  protoplasm  stains  brown; 
the  rest  of  the  cell  remains  unstained.     Note  .the 
absence  of  any  blue  coloration;  starch  is  therefore 
not  present. 

6.  Treat  another  specimen  with  potash  solution,  running 
it  in  as  before :  this  reagent  dissolves  out  the  proto- 
plasm, leaving  the  sac  unaltered. 

7.  [Sow  a  few  yeast-cells  in  Pasteur's  solution  in  a  moist 
chamber  and  keep  them  under  observation  from  day  to 
day ;  watch  their  growth  and  multiplication.] 

8.  [Endogenous  division:  take  some  dry  German  yeast; 
suspend  it  in  water  and  shake  so  as  to  wash  it.     Let 
the  mixture  stand  for  half  an  hour :  pour  off  the  super- 

.:  natant  fluid,  and,  with  a  camel's  hair  pencil,  spread  out 

the  creamy  deposit  in  a  thin  layer  on  fresh  cut  potato 
slices  or  on  a  plate  of  plaster  of  Paris,  and  place  with 
wet  blotting  paper  under  a  bell-jar:  examine  from  day 
to  day  with  a  very  high  power  (800  diam.)  for  asco- 
spores,  which  will  probably  be  found  on  the  eighth  or 
ninth  day.] 

B.     PHYSIOLOGY. 

(Conditions  and  results  of  the  vital  activity  of  Torula.) 
i.     Sow  a  fair-sized  drop  of  yeast  in — 

a.  Distilled  water. 

b.  10  per  cent,  solution  of  sugar  in  water. 

c.  Pasteur's  fluid  without  the  sugar. 


r.]  YEAST.  9 

d.     Pasteur's  fluid  with  sugar. 
[e.     Mayer's  pepsin  solution1.] 

Keep  all  at  about  35°  C.,  and  compare  the  growth  of  the 
yeast,  as  measured  by  the  increase  of  the  turbidity  of  the 
fluid,  in  each  case.  "  a  "  will  hardly  grow  at  all,  "  b"  better, 
'V  better  still,  "d"  well,  and  "e"  best  of  all.  Note  that 
bubbles  of  gas  are  plentifully  evolved  from  both  the  so- 
lutions which  contain  sugar. 

That  any  growth  at  all  takes  place,  in  the  case  of 
experiments  a  and  £,  is  due  to  the  fact  that  the  drop  of 
yeast  added  contains  nutritious  material  sufficient  to  provide 
for  that  amount  of  growth. 

2.      Prepare  two  more  specimens  of  "  d"  and  keep  one 
in  a  cold — the  other  in  a  warm  (35°  C.)  place,  but 
otherwise  under  like  conditions .   Compare  the  growth 
of  the  yeast  in  the  two  cases  ;  it  is  much  greater  in . 
the  specimen  kept  warm. 

.3.  Prepare  two  more  specimens  of  "d";  keep,  both 
warm,  but  one  in  darkness,  the  other  exposed  to  the 
light:  that  in  the  dark  will  grow  as  well  as  the  other ; 
sunlight  is  therefore  not  essential  to  the  growth  of 
Torula. 

4.  Sow  some  yeast-cells  in  Pasteur's  solution  in  a  flask, 
the  neck  of  which  is  closed  by  a  plug  of  cotton 
wool,  and  boil  for  five  minutes;  then  set  it  aside; 
no  signs  of  vitality  will  afterwards  be  manifested  by 
the  yeast  in  the  flask ;  it  is  killed  by  exposure  to 
this  temperature. 

1  Mayer's  solution  (with  pepsin)  = 

1 5  per  cent,  solution  of  sugar-candy      20  cc. 

Dihydropotassic  phosphate  o'  i  grm. 

Calcic  phosphate o'  I  grm. 

Magnesic  sulphate o'  i  grm. 

Pepsin 0-23  grm. 


[o  ELEMENTARY  BIOLOGY.  [CHAP.  i. 

5.  [Take  two  test  tubes;  in  one  place  some  yeast,  with 
Pasteur's  solution  containing  sugar ;  in  the  other  place 
baryta  water,  and  then  connect  the  two  test  tubes  by 
tightly  fitting  perforated  corks  and  a  bent  tube  passing 
from  above  the  surface  of  the  fluid  in  the  first  tube  to 
the  bottom  of  the  baryta  water  in  the  second ;  pass  a 
narrow  bent  tube,  open  at  both  ends,  through  the  cork 
of  the  baryta  water  tube,  so  that  its  outer  end  dips  just 
below  the  surface  of  some  solution  of  potash1.    All  gas 
formed  in  the  first  tube  will  now  bubble  through  the 
baryta  water  in  the  second,  and,  from  thence,  any  that 
is  not  absorbed  will  pass  out  through  the  potash  into 
the  air.     An  abundant  precipitate  of  barytic  carbonate 
will  be  formed  which  can  be  collected  and  tested.     The 
fermenting  fluid,  therefore,  evolves  carbonic  anhydride.] 

6.  [Grow  some  yeast  in  Pasteur's  solution  (with  sugar),  in  a 
nearly  closed  vessel  (say  a  bottle  with  a  cork  through 
which  a  long  narrow  open  tube  passes) :  as  soon  as  the 
evolution  of  gas  seems  to  have  ceased,  distil  the  fluid  in 
a  water  bath  and  condense  and  collect  the  first  fifth 
that    comes    over:    redistil  this  after  saturation  with 
potassic  carbonate,  and  test  the  distillate  for  alcohol  by 
its  odour  and  inflammability,  and  by  the  sulphuric  acid 
and  potassic  dichromate  test] 

7.  [Determine  that  heat  is  evolved  by  a  fluid  in  which 
active  alcoholic  fermentation  is  going  on.    Place  200  cc. 
of  fresh  yeast  in  a  flask,  and  add  I  litre  of  Pasteur's 
fluid  with  sugar :  put  another  litre  of  the  fluid  alone  in 
a  similar  flask,  cover  each  flask  with  a  cloth  and  place 
the  two  side  by  side  in  a  place  protected  from  draughts. 
When  gas  begins  to  be  actively  evolved  from  the  yeast- 
containing  solution,  take  the  temperature  of  the  fluid  in 
each  flask  with  a  good  thermometer ;  the  temperature  of 
the  one  in  which  fermentation  is  going  on  will  be  found 
the  higher.] 

1  The  object  of  the  potash  is  to  shield  the  baryta  water  from  any 
carbonic  anhydride  that  may  be  in  the  atmosphere. 


II. 

PROTOCOCCUS  (Protococcus  pluvialis). 

IF  the  mud  which  accumulates  in  roof-gutters,  water- 
butts,  and  shallow  pools,  be  collected,  it  will  be  found  to 
contain,  among  many  other  organisms,  specimens  of  Pro- 
tococcus. In  one  of  the  two  conditions  in  which  it  occurs, 
Protococcus  is  a  spheroidal  body  -^i^-  to  10^00  of  an  inch  in 
diameter,  composed,  like  Torula,  of  a  structureless  tough 
transparent  wall,  inclosing  viscid  and  granular  protoplasm. 
The  chief  solid  constituent  of  the  cell-wall  is  cellulose.  The 
protoplasm  contains  a  nitrogenous  substance,  doubtless  of  a 
proteinaceous  nature,  though  its  exact  composition  has  not 
been  determined,  and  indications  of  starchy  matter  are 
sometimes  to  be  found  in  it.  Either  diffused  through  it,  or 
collected  in  granules,  is  a  red  or  green  colouring  matter 
(Chlorophyll).  Individual  Protococci  may  b.e  either  green 
or  red ;  or  half  green  and  half  red ;  or  the  red  and  green 
colours  may  coexist  in  any  other  proportion. 

In  addition  to  the  single  cells,  others  are  found  divided 
by  partitions,  continuous  with  the  cellulose  wall,  into  two  or 
more  portions,  and  the  cells  thus  produced  by  fission  become 
separate,  and  grow  to  the  size  of  that  form  from  which  they 
started.  In  this  manner  Protococcus  multiplies  with  very 
great  rapidity.  Multiplication  by  gemmation  in  the  mode 
observed  in  Torula  is  said  to  occur,  but  is  certainly  of  rare 
occurrence. 


12  ELEMENTARY  BIOLOGY.  [CHAP. 

The  influence  of  sunlight  is  an  essential  condition  of  the 
growth  and  multiplication  of  Protococcus ;  under  that  in- 
fluence, it  decomposes  carbonic  anhydride,  appropriates  the 
carbon,  and  sets  oxygen  free.  It  is  this  power  of  obtaining 
the  carbon  which  it  needs  from  carbonic  anhydride,  which 
is  the  most  important  distinction  of  Protococcus,  as  of  all 
plants  which  contain  chlorophyll,  from  Torula  and  the  other 
Fungi. 

As  Protococcus  flourishes  in  rain-water,  and  rain-water 
contains  nothing  but  carbonic  anhydride,  which  it  absorbs 
along  with  other  constituents  of  the  atmosphere,  ammonium 
salts  (usually  ammonium  nitrate,  also  derived  from  the  air) 
and  minute  portions  of  earthy  salts  which  drift  into  it  as 
dust,  it  follows  that  it  must  possess  the  power  of  constructing 
protein  by  rearrangement  of  the  elements  supplied  to  it  by 
their  compounds.  Torula,  on  the  other  hand,  is  unable  to 
construct  protein  matter  out  of  such  materials  as  these. 

Another  difference  between  Torula  and  Protococcus  is 
only  apparent :  Torula  absorbs  oxygen  and  gives  out  car- 
bonic anhydride ;  while  Protococcus,  on  the  contrary,  absorbs 
carbonic  anhydride  and  gives  out  oxygen.  But  this  is  true 
only  so  long  as  the  Protococcus  is  exposed  to  sunlight.  In 
the  dark,  Protococcus,  like  all  other  living  things,  undergoes 
oxidation  and  'gives  off  carbonic  anhydride;  and  there  is 
every  reason  to  believe  that  the  same  process  of  oxidation 
and  evolution  of  carbonic  anhydride  goes  on  in  the  light, 
but  that  the  loss  of  oxygen  is  far  more  than  covered  by  the 
quantity  set  free  by  the  carbon-fixing  apparatus,  which  is  in 
some  way  related  to  the  chlorophyll. 

The  still  condition  of  Protococcus,  just  described,  is  not 
the  only  state  in  which  it  exists.  Under  certain  circum- 
stances, a  Protococcus  becomes  actively  locomotive.  The 
protoplasm  withdraws  itself  from  the  cell- wall  at  all  but  two 


IL]  PROTOCOCCUS.  13 

points,  where  it  protrudes  through  the  wall  in  the  form  of 
long  vibratile  filaments  or  cilia,  and  by  the  lashing  of  these 
cilia  the  cell  is  propelled  with  a  rolling  motion  through  the 
water.  The  movement  of  the  cilia  is  so  rapid,  and  their 
substance  is  so  transparent  and  delicate,  that  they  are  invisi- 
ble until  they  begin  to  move  slowly,  or  are  treated  with 
reagents,  such  as  iodine,  which  colour  them. 

Not  unfrequently  the  cell-wall  eventually  vanishes,  and 
the  naked  protoplasm  of  the  cell  swims  about,  and  may 
undergo  division  and  multiplication  in  this  state.  Sooner 
or  later,  the  locomotive  form  draws  in  its  cilia,  becomes 
globular,  and,  throwing  out  a  cellulose  coat,  returns  to  the 
resting  state. 

For  reasons  similar  to  those  which  prove  the  vegetable 
nature  of  Torula,  Protococcus  is  a  plant,  although,  in  its 
locomotive  condition,  it  is  curiously  similar  to  the  Monads 
among  the  lowest  forms  of  animal  life.  But  it  is  now  known 
that  many  of  the  lower  plants,  especially  in  the  group  of 
Alga,  to  which  Protococcus  belongs,  give  rise,  under  certain 
circumstances,  to  locomotive  bodies  propelled  by  cilia,  like 
the  locomotive  Protococcus,  so  that  there  is  nothing  anomalous 
in  the  case  of  Protococcus. 

Like  the  yeast-plant,  Protococcus  retains  its  vitality  after 
it  has  been  dried.  It  has  been  preserved  for  as  long  as  two 
years  in  the  dry  condition,  and  at  the  end  of  that  time  has 
resumed  its  full  activity  when  placed  in  water.  The  wide 
distribution  of  Protococcus  on  the  tops  of  houses  and  else- 
where, is  thus  readily  accounted  for  by  the  transport  of  the 
dry  Protococci  by  winds. 


i4  ELEMENTARY  BIOLOGY.  [CHAP. 

LABORATORY  WORK. 
A.     MORPHOLOGY. 

a.    Resting  or  stationary  Protococcus. 

1.  Spread  out  in  water  some  mud  from   a  gutter  or 
similar  locality,  and  put  on  a  cover-glass.     Look  for 
the  red    or    green    protococcus    cells   with   a  low 
power.     Having  found  some,  put  on  a  high  power 
and  make  out  the  following  points. 

Size;  (measure) — very  variable. 

Form;    more    or   less    spheroidal,   with   individual 

variations. 
Structure;  sac — protoplasm — sometimes  a  vacuole — 

sometimes    apparently    a    nucleus.     (Compare 

Torula,  I.  A.  2.  b.) 

Colour;  generally  green — sometimes  red — sometimes 
half  and  half — sometimes  centre  red,  periphery 
green — the  colouring  matter  always  in  the  pro- 
toplasm only — most  frequently  diffused,  but 
sometimes  in  distinct  granules,  or  oily  looking 
drops. 

2.  Note  especially  the  following  forms  of  cell— 
(i.      The  primitive  or  normal  form. 

Roundish  cells,  with  a  cellulose  sac,  and  unseg- 
mented  granular  contents.  Draw  several  carefully 
to  scale.  Apply  the  methods  of  mechanical  and 
chemical  analysis  detailed  for  Torula.  (I.  A.  3.  4. 
5.  6.)  Note  that  iodine  in  some  cells  produces  a 
blue  coloration  by  its  action  on  the  red  matter 
present.  Treat  a  specimen  with  strong  iodine 
solution  and  then  with  sulphuric  acid  (75  per 
cent.)  :  the  sac  will  become  stained  blue. 


ii.]  PROTOCOCCUS.  ,5 

b.     Cells  multiplying  by  fission : 

a.  Simple  fission.  The  cell  elongates,  and  the 
protoplasm  divides  into  two  across  its  longer 
axis,  and  then  a  partition  is  formed  sub- 
dividing the  sac;  the  halves  either  separate 
at  once,  and  each  rounds  itself  off  and  be- 
comes an  independent  cell ;  or  one  or  both 
halves  again  divide,  in  a  similar  way,  before 
they  separate,  and  so  three  or  four  new  cells 
are  produced. 
/?.  Cells  multiplying  by  budding,  like  Torula;  rare. 

b.    Motile  stage. 

a.      Mount  a  drop  of  water  containing  motile  Proto- 
coccus,  and  examine  with  a  high  power.     Note 
the  actively  locomotive  green  bodies,  of  which 
two  varieties  can  be  distinguished. 
a.      Cells   like  the   stationary  ones  in  size,  and 
apparently  directly  formed  from  them.     Each 
possesses  a  structureless  colourless  sac,  sur- 
rounding the  coloured  protoplasm,  but   the 
latter  has  shrunk  away  from  the  sac  at  most 
points. 

Note  in  various  specimens — The  two  cilia 
prolonged  from  the  protoplasm  through  aper- 
tures in  the  sac ;  their  motionless  part  within 
the  sac;  their  vibratile  portion  outside  it. 
The  colourless  thin  external  layer  of  the 
protoplasm  collected  into  a  little  heap  at  the 
point  from  whence  the  cilia  arise.  The  deli- 
cate colourless  processes  radiating  from  the 
outer  protoplasmic  layer  to  the  interior  of  the 
sac.  The  colour — usually  green,  but  frequently 
one  bright  red  spot  is  present. . 

f^  or  THE 

f    UNIVERSITY 


V 


j 6  ELEMENTARY  BIOLOGY.  [CHAP.  n. 

(3.  Cells  much  like  the  above  if  the  cellulose 
sac  were  removed,  and  the  radiating  processes 
extending  to  it  from  the  protoplasm  with- 
drawn. 

b.  Try  to  find  specimens  in  which  the  movements 
are  becoming   sluggish,    and   see   the   cilia  in 
motion. 

c.  Stain  with  iodine  :  this  kills  the  cells,  and  stops 

their  movements  ;  and  frequently  renders  the 
cilia  very  distinct. 

[B.    PHYSIOLOGY. 

Get  some  water  that  is  quite  green  from  containing  a 
large  quantity  of  Protococcus ;  introduce  some  of  it 
into  two  tubes  filled  with  and  inverted  over  mercury, 
and  pass  a  small  quantity  of  carbonic  anhydride  into 
each:  keep  one  tube  in  the  dark  and  place  the  other 
in  bright  sunlight  for  some  hours.  Then  measure  the 
gas  in  each  tube  and  afterwards  introduce  a  fragment 
of  caustic  potash  into  each ;  the  gas  from  the  specimen 
kept  in  the  dark  will  be  more  or  less  completely  ab- 
sorbed (=  carbonic  anhydride),  that  from  the  other 
will  not  be  absorbed  by  the  potash  alone,  but  will  be 
absorbed  on  the  further  introduction  of  a  few  drops  of 
solution  of  pyrogallic  acid  (  =  oxygen).  Protococcus, 
therefore,  in  the  sunlight,  takes  up  carbonic  anhydride 
and  evolves  oxygen.  A  comparative  experiment  may 
be  made  with  a  third  tube  containing  water  but  no 
Protococcus.] 


III. 

THE  PROTEUS  ANIMALCULE   (Anueba). 
COLOURLESS  BLOOD  CORPUSCLES. 

Amoeba  are  minute  organisms  of  very  variable  size  which 
occur  in  stagnant  water,  in  mud,  and  even  in  damp  earth, 
and  are  frequently  to  be  obtained  by  infusing  any  animal 
matter  in  water  and  allowing  it  to  evaporate  while  exposed 
to  direct  sunlight. 

An  Amoeba  has  the  appearance  of  a  particle  of  jelly, 
which  is  often  more  or  less  granular  and  fluid  in  its  central 
parts,  but  usually  becomes  clear  and  transparent,  and  of  a 
firmer  consistency,  towards  its  periphery.  Sometimes  Amcebcs 
are  found  having  a  spherical  form  and  encased  in  a  struc- 
tureless sac,  and  in  this  encysted  state  they  exhibit  no 
movements.  More  commonly,  they  present  incessant  and 
frequently  rapid  changes  of  form,  whence  the  name  of 
"Proteus  Animalcule"  given  to  them  by  the  older  ob- 
servers; and  these  changes  of  form  are  usually  accompanied 
by  a  shifting  of  position,  the  Amoeba  creeping  about  with 
considerable  activity,  though  with  no  constancy  of  direction. 

The  changes  of  form,  and  the  movements,  are  effected  by 
the  thrusting  out  of  lobe-like  prolongations  of  the  peripheral 
part  of  the  body,  which  are  termed  pseudopodia,  sometimes 
from  one  region  and  sometimes  from  another*  Occasionally, 
a  particular  region  of  the  body  is  constantly  free  from 
pseudopodia,  and  therefore  forms  its  hindmost  part  when 
M.  a 


1 8  ELEMENTARY  BIOLOGY.  [CHAP. 

it  moves.  Each  pseudopodium  is  evidently,  at  first,  an 
extension  of  the  denser  clear  substance  (ectosarc)  only; 
but  as  it  enlarges,  the  central,  granular,  more  fluid  sub- 
stance flows  into  its  interior,  often  with  a  sudden  rush. 

In  some  Amoeba  a  clear  space  makes  its  appearance,  at 
intervals,  in  a  particular  region  of  the  ectosarc,  and  then 
disappears  by  the  rapid  approach  of  its  walls.  After  a 
while,  a  small  clear  speck  appears  at  the  same  spot  and 
slowly  dilates  until  it  attains  its  full  size,  when  it  again 
rapidly  disappears  as  before.  Sometimes  two  or  three 
small  clear  spots  arise  close  together,  and  run  into  one 
another  to  form  the  single  large  cavity.  The  structure 
thus  described  is  termed  the  contractile  vesicle  or  vacuolc, 
and  its  rhythmical  systole  and  diastole  often  succeed  one 
another  with  great  regularity.  Nothing  is  certainly  known 
respecting  its  function,  nor  even  whether  it  does  or  does 
not  communicate  with  the  exterior,  and  thus  pump  water 
into  and  out  of  the  body  of  the  Amoeba,  though  there  is 
some  reason  to  think  that  this  may  be  the  case. 

Very  frequently  one  part  of  the  Amoeba  exhibits  a 
rounded  or  oval  body,  which  is  termed  the  nucleus.  This 
structure  sometimes  has  a  distinctly  vesicular  character,  and 
contains  a  rounded  granule  called  the  nucleates. 

The  gelatinous  body  of  the  Amceba  is  not  bounded  by 
anything  that  can  be  properly  termed  a  membrane ;  all 
that  can  be  said  is,  that  its  external  or  limitary  layer  is 
of  a  somewhat  different  constitution  from  the  rest,  so  that 
it  acquires  a  certain  appearance  of  distinctness  when  it  is 
acted  upon  by  such  reagents  as  acetic  acid,  or  when  the 
animal  is  killed  by  raising  the  temperature  to  45°  C.  Physic- 
ally, the  ectosarc  might  be  compared  to  the  wall  of  a 
soap-bubble,  which,  though  fluid,  has  a  certain  viscosity, 
which  not  only  enables  its  particles  to  hold  together  and 


in.]  THE  PROTEUS  ANIMALCULE.  19 

form  a  continuous  sheet,  but  permits  a  rod  to  be  passed 
into  or  through  the  bubble  without  bursting  itj  the  walls 
closing  together,  and  recovering  their  continuity,  as  soon 
as  the  rod  is  drawn  away. 

It  is  this  property  of  the  ectosarc  of  the  Amoeba  which 
enables  us  to  understand  the  way  in  which  these  animals 
take  in  and  throw  out  again  solid  matter,  though  they  have 
neither  mouth,  anus,  nor  alimentary  canal.  The  solid  body 
passes  through  the  ectosarc,  which  immediately  closes  up 
and  repairs  the  rent  formed  by  its  passage.  In  this  manner, 
the  Amcebcz  take  in  the  small,  usually  vegetable,  organisms, 
which  serve  them  for  food,  and  subsequently  get  rid  of  the 
undigested  solid  parts. 

The  chemical  composition  of  the  bodies  of  the  Amcebcz 
has  not  been  accurately  ascertained,  but  they  undoubtedly 
consist,  in  great  measure,  of  water  containing  a  protein  com- 
pound, and  are  similar  to  other  forms  of  protoplasm.  They 
absorb  oxygen  and  give  out  carbonic  acid,  and  the  presence 
of  free  oxygen  is  necessary  to  their  existence.  When  the 
medium  in  which  they  live  is  cooled  down  to  the  freezing 
point  their  movements  are  arrested,  but  they  recover  when 
the  temperature  is  raised.  At  a  temperature  of  about  35°  C. 
their  movements  are  arrested,  and  they  pass  into  a  condition 
of  "  heat-stiffening,"  from  which  they  recover  if  that  tem- 
perature is  not  continued  too  long ;  at  40°  to  45°  C.  they 
are  killed. 

Electric  shocks  of  moderate  strength  cause  Amoeba  at 
once  to  assume  a  spherical  still  form,  but  they  recover  after 
a  while.  Strong  shocks  kill  them. 

Not  unfrequently,  an  active  Amceba  becomes  still  spon- 
taneously, acquires  a  rounded  form,  and  secretes  a  structure- 
less case  or  cyst,  in  which  it  remains  enclosed  for  a  shorter 
or  longer  period. 

2 — 2 


•20  ELEMENTARY  BIOLOGY.  [CHAP. 

If  Amoeba  are  not  to  be  found,  their  nature  may  be 
understood  by  the  examination  of  bodies,  in  many  respects 
very  similar  to  them,  which  occur  in  the  blood  of  all  verte- 
brate and  most  invertebrate  animals,  and  are  known  as  the 
'colourless  corpuscles.1  They  are  to  be  met  with  in  abun- 
dance in  a  fresh-drawn  drop  of  human  blood.  In  such  a 
drop,  after  the  red  corpuscles  have  run  into  rolls,  irregular 
bodies  will  be  seen  here  and  there  in  the  meshes  of  the 
rolls.  If  one  of  these  bodies  is  carefully  watched  it  will 
be  seen  to  undergo  changes  of  form  of  the  same  character 
as  those  exhibited  by  Amoeba,  and  these  motions  become 
much  more  active  if  the  drop  is  kept  at  the  temperature  of 
the  body  by  means  of  a  hot  stage.  Each  corpuscle  is,  in 
fact,  a  mass  of  protoplasm  containing  a  nucleus,  and  the 
protoplasm  sends  out  pseudopodia  which  are  strictly  com- 
parable to  those  of  Amoeba.  The  colourless  corpuscles, 
however,  possess  no  contractile  space. 

The  colourless  corpuscles  of  the  blood  of  some  of  the 
cold-blooded  vertebrates,  such  as  Frogs  and  Newts,  may  be 
kept  alive  for  many  weeks  in  serum  properly  protected  from 
evaporation;  and  if  finely  divided  colouring  matter,  such 
as  indigo,  is  supplied  to  them,  either  in  the  body  or  out  of 
it,  they  take  it  into  their  interior  in  the  same  way  as  true 
Amoebae  would.  In  the  earliest  condition  of  the  embryo, 
the  whole  body  is  composed  of  such  nucleated  cells  as  the 
colourless  corpuscles  of  the  blood  ;  and  the  colourless  cor- 
puscles must  be  regarded  as  simply  the  progeny  of  such 
cells,  which  have  not  become  metamorphosed,  and  have 
retained  the  characteristics  of  the  lowest  and  most  rudi- 
mentary forms  of  animal  life. 

The  Amceba  is  an  animal,  not  because  of  its  contractility 
or  power  of  locomotion,  but  because  it  never  becomes  en- 
closed within  a  cellulose  sac,  and  because  it  is  devoid  of 


in.]  THE  PROTEUS  ANIMALCULE.  21 

the  power  of  manufacturing  protein  from  bodies  of  a  com- 
paratively simple  chemical  composition.  The  Amoeba  has 
to  obtain  its  protein  ready  made,  in  which  respect  it  re- 
sembles all  true  animals,  and  therefore  is,  like  them,  in  the 
long  run,  dependent  for  its  existence  upon  some  form  or 
other  of  vegetable  life. 


LABORATORY  WORK. 

A.     AMCEBA. 

Place  a  drop  of  water  containing  Amccbtz  on  a  slide, 
cover  with  a  cover  glass,  avoiding  pressure,  and  search  over 
with  Jinch  obj. :  having  found  an  Amceba,  examine  with  a 
higher  power. 

1.  Size:  differing  considerably  in  different  specimens. 
Measure.     . 

2.  Outline :  irregular,  produced  into  a  number  of  thick 
rounded   eminences  (pseudopodid)   which  are    con- 
stantly undergoing  changes  :  sketch  it  at  intervals  of 
five  seconds. 

3.  Structure: 

a.  Outer  hyaline  border  (ectosarc\  tolerably  sharply 
marked  off:  granular  layer  (endosarc)  inside  this, 
gradually  passing  into  a  more  fluid  central  part. 

b.  Nucleus :  (absent  in  some  specimens) ;  a  round- 
ish more  solid-looking  particle,  which  does  not 
change  its  form. 

c.  Contractile  vesicle :  in  the  ectosarc  note  a  round- 
ish clear  space  which  disappears  periodically, 
and  after  a  short  time  reappears ;  its  slow  diastole 
— rapid  systole.     Not  present  in  all  specimens. 


22  ELEMENTARY  BIOLOGY.  [CHAP. 

d.     Foreign  bodies  (swallowed) ;  Diatom  cases,  Des- 
midice,  &c. 

4.  Movements : 

a.  Watch  the  process  of  formation  of  a  pseudcpo- 

dium.  A  hyaline  elevation  at  first ;  then,  as  it 
increases  in  size,  currents  carrying  granules  flow 
into  it. 

b.  Locomotion :    watch  the   process, — a  pseudo- 
podium   is   thrown  out,  then   the   rest  of  the 
body  appears  to  flow  up  to  it,  and  the  process 
is  repeated. 

c.  If  the  opportunity  presents  itself,  watch  the  pro- 
cess of  the  ingestion  of  solid  matters. 

d.  [Observe  the  movements  on  the  hot  stage ;  warmth 
at  first  accelerates  the  movements,  but  as  the  tem- 
perature approaches    40°  C.  they  cease,   and  the 
whole  mass  remains  as  a  motionless  sphere.] 

e.     [Effects  of  electrical  shocks  on  the  movements.] 

5.  Mechanical  Analysis :  crush.     The  whole  collapses, 
except  sometimes  the  nucleus,  and  even  that  after  a 
time   disappears :  there   is  no   trace   of  a   distinct 
resisting  outer  sac. 

6.  Chemical  Analysis :  Treat  with  magenta  and  iodine. 
The  whole  stains,  and  there  is  no  unstained  envelop- 
ing sac.     Iodine  as  a  rule  produces  no  blue  colora- 
tion ;  when  blue  specks  become  visible  it  is  probable 
that    the    starch    which    they    indicate    has    been 
swallowed. 

7.    [Look  for  encysted  specimens :  and  for  specimens  which 
are  undergoing  fission.] 


in.]  THE  PROTEUS  ANIMALCULE.  *$ 

8.  Another  form  of  Amoeba  is  not  unfrequently  found 
which  differs  from  that  just  described  in  being  much 
less  coarsely  granular,  and  in  having  no  well-defined 
ectosarc  and  endosarc,  and  also  in  having  much 
longer,  more  slender  and  pointed  pseudopodia. 
Another  common  form  progresses  rapidly  with  a 
slug-like  movement,  only  throwing  out  pseudopodia 
at  its  anterior  end. 

B.     WHITE  BLOOD-CORPUSCLES,  (human). 

Prick  your  finger  and  press  out  a  drop  of  blood  :  spread 
out  on  a  slide  under  a  coverslip,  avoiding  pressure,  and 
surround  the  margin  of  the  coverglass  with  oil.  Neglect 
the  pale  yellow  homogeneous  (red)  corpuscles,  and  examine 
the  much  less  numerous,  granular,  colourless,  ones. 

Note  their — 

1.  Size:  (measure). 

2.  Form:  changing  much  like  that  of  the  Amoeba,  but 
less  actively.     Draw  at  intervals  of  ten  seconds. 

3.  Structure:  Some  more  and  some  less  granular ;  but 
no  distinct  ectosarc,  endosarc,  and  vacuole  as  in  the 
Amoeba.    Nucleus  rarely  visible  in  the  fresh  state. 

.    No  contractile  vesicle. 

4.  Treat  with   dilute   acetic   acid  :    the    granules   are 
cleared  up,  and  a  nucleus  is  brought  into  view  in  a 
more  or  less  central  position.     If  the  acetic  acid  has 
been  too  strong  the  nucleus  will  be  constricted  and 
otherwise  distorted. 

5.  Stain  with  magenta,  and  iodine ;  the  whole  becomes 
coloured,  the  nucleus  most  intensely. 

6.  Place  on  the  hot  stage,  and  gradually  warm  up  to 
50°  C.     The  movements  are  at  first  rendered  more 


24  ELEMENTARY  BIOLOGY.  [CHAP.  in. 

active,  but  ultimately  cease,  the  pseudopodia-like 
processes  being  all  retracted  and  the  whole  forming 
a  motionless  sphere. 

Let  the  specimen  cool  again  ;  the  movements  are 
not  resumed ;  the  protoplasm  having  passed  into  a 
state  of  permanent  coagulation  or  rigidity. 

7.      Repeat  the  above  observations  on  the  white  blood- 
corpuscles  of  the  frog  or  newt. 


IV. 
BACTERIA. 

UNDER  the  general  title  of  Bacterium  a  considerable  variety 
of  organisms,  for  the  most  part  of  extreme  minuteness,  are 
included. 

They  may  be  denned  as  globular,  oblong,  rod-like  or 
spirally  coiled  masses  of  protoplasmic  matter  enclosed  in  a 
more  or  less  distinct  structureless  substance,  devoid  of 
chlorophyll  and  multiplying  by  transverse  division.  The 
smallest  are  not  more  than  aooootn  of  an  inch  in  diameter, 
so  that  under  the  best  microscopes  they  appear  as  little 
more  than  mere  specks,  and  even  the  largest  have  a  thick- 
ness of  little  more  than  10^o0th  of  an  inch,  though  they 
may  be  very  long  in  proportion.  Many  of  them  have,  like 
Protococcus,  two  conditions — a  still  and  an  active  state.  In 
their  still  condition,  however,  they  very  generally  exhibit  that 
Brownian  movement  which  is  common  to  almost  all  very 
finely  divided  solids  suspended  in  a  fluid.  But  this  motion 
is  merely  oscillatory,  and  is  readily  distinguishable  from  the 
rapid  translation  from  place  to  place  which  is  effected  by 
the  really  active  Bacteria. 

In  one  of  the  largest  forms,  Spirillum  vohttans,  it  has 
been  possible  to  observe  the  cilia  by  which  the  movement 
is  effected.  In  this  there  is  a  cilium  at  each  end  of  the 
spirally  coiled  body.  No  such  structure,  however,  can  be 
made  out  in  the  straight  Bacteria,  and  it  remains  doubtful 
whether  they  possess  cilia  which  are  too  fine  to  be  rendered 


i6  ELEMENTARY  BIOLOGY.  [CHAP. 

visible  by  our  microscopes,  or  whether  their  movements  are 
due  to  some  other  cause.  Many  forms,  such  as  the  Vibriones, 
so  common  in  putrefying  matters,  appear  obviously  to  have 
a  wriggling  or  serpentiform  motion,  but  this  is  an  optical 
illusion.  In  this  Bacterium,,  as  in  all  others,  the  body  does 
not  rapidly  change  its  form ;  but  its  joints  are  bent  zig-zag- 
wise,  and  the  rotation  of  the  zig-zag  upon  its  axis,  as  it 
moves,  gives  rise  to  the  appearance  of  undulatory  contrac- 
tion. A  cork-screw  turned  round,  while  its  point  rests 
against  the  finger,  gives  rise  to  just  the  same  appearance. 

Bacteria,  in  the  still  state,  very  often  become  surrounded 
by  a  gelatinous  matter,  which  seems  to  be  thrown  out  by 
their  protoplasmic  bodies,  and  to  answer  to  the  cell-wall  of 
the  resting  Protococcus.  This  is  termed  the  Zoogloea  form  of 
Bacterium. 

Bacteria  grow  and  multiply  in  Pasteur's  solution  (with- 
out sugar)  with  extreme  rapidity,  and,  as  they  increase  in 
number,  they  render  the  fluid  milky  and  opaque.  Their 
vital  actions  are  arrested  at  the  freezing  point.  They  thrive 
best  in  a  temperature  of  about  30°  C.  but,  in  most  fluids, 
they  are  killed  by  a  temperature  of  60°  C.  (140°  F.). 

In  all  these  respects  Bacteria  closely  resemble  Torulce; 
and  a  further  point  of  resemblance  lies  in  the  circumstance 
that  many  of  them  excite  specific  fermentative  changes  in 
substances  contained  in  the  fluid  in  which  they  live,  just  as 
yeast  excites  such  changes  in  sugar. 

All  the  forms  of  putrefaction  which  are  undergone  by 
animal  and  vegetable  matters  are  fermentations  set  up  by 
Bacteria  of  different  kinds.  Organic  matters  freely  exposed 
to  the  air  are,  in  themselves,  nowise  unstable  bodies,  and, 
if  due  precautions  have  been  taken  to  exclude  Bacteria, 
they  do.. not  putrefy,  so  that,  as  has  been  well  remarked, 
"  putrefaction  is  a  concomitant  not  of  death,  but  of  life." 


IV.]  BACTERIA.  17 

Bacteria,  like  Torula  and  Protococci,  are  not  killed  by 
drying  up,  and  from  their  excessive  minuteness  they  must 
be  carried  about  still  more  easily  than  Torulct  are.  In 
fact  there  is  reason  to  believe  that  they  are  very  widely 
diffused  through  the  air,  and  that  they  exist  in  abundance 
in  all  ordinary  water  and  on  the  surface  of  all  vessels  that 
are  not  chemically  clean.  They  may  be  readily  filtered  off 
from  the  air,  however,  by  causing  it  to  pass  through  cotton 
wool. 


LABORATORY  WORK. 

1.  Infuse  some  hay  in  warm  water  for  half  an  hour — 
filter,  and  set  aside  the  filtrate:   note  the   changes 
which  go  on  in  it — at  first  clear,  in  24  or  36  hours  it 
becomes  turbid;  later  on,  a  scum  forms  on  the  sur- 
face and  the  infusion  acquires  a  putrefactive  odour. 

2.  Rub  some  gamboge  down  in  water  and  examine  a 
drop  of  the  mixture  with  a  high  power:  avoid  all 
currents  in  the  fluid  and  watch  the  Brownian  move- 
ments;  note  that  they  are  simply  oscillatory — not 
translative. 

3.  Take  a  drop  of  fluid  from  a  turbid  hay  infusion — 
and  examine  it,  using  the  highesj  power  you  have; 
in  it  will  be  found  multitudes  of 

Moving  Bacteria.    Note  their — 

a.  Form;  elliptic  or  rodlike — sometimes  forming 
short  (2 — 8)  jointed  rows. 

b.  Size;  breadth,  very  small  but  pretty  constant; 
length,  varying,  but  several  times  greater  than 
their  breadth:  measure. 


28  ELEMENTARY  BIOLOGY.  [CHAP. 

c.  Structure;    an    outer    more    transparent    layer 
enveloping  less  transparent  matter:  in  the  com- 
pound forms  the  envelope  appears  only  where 
two  joints  come  in  contact,  so  that  the  rod 
looks  as  if  made  up  of  alternating  transparent 
and  more  opaque  substances. 

d.  Movements;  some  vital,  and  some  purely  phy- 
sical (Brownian].     The  former  various  but  pro- 
gressive :  the  latter,  a  rotatory  movement  round 
a  stationary  centre;  study  it  in  a  drop  of  boiled 
infusion  in  which  the  Bacteria  are  all  dead. 

4.  Treat   with    iodine — only  the  more   opaque  parts 
stain ;  probably  then  we  have  to  do  with  protoplasm, 
enveloped  in  nonprotoplasmic  matter. 

5.  Eesting  Bacteria.     (Zoogloea-stage.) 

a.  Examine  the  scum  from  the  surface  of  a  hay 
infusion;  it  exhibits  myriads  of  motionless  Bac- 
teria, embedded  in  gelatinous  material. 

b.  Treat  with  iodine;  the  Bacteria  stain  as  before  : 
the    gelatinous   uniting   material    remains    un- 
stained. 

6.  Mixed  with  the  Bacteria  proper,  both  in  the  pellicle 
and  the  fluid  beneath,  may  be  found  the  following 
forms  of  living  beings. 

a.  Micrococcus.     Bodies  much  like  Bacteria,  but 
short  and  rounded,  and  occurring  singly,  or  in 
bead-like  rows.    They  may  be  found  free  or  in  a 
Zoogloea  stage. 

b.  Bacillus.     Threads  composed  of  straight  cylin- 
drical joints  much  longer  than  those  of  Bacteria 


iv.]  BACTERIA.  79 

but  of  a  similar  structure :  they  are  always  free- 
swimming. 

c.  Vibrio.     Like  Bacillus,  but  with  bent  joints. 

d.  Spirillum.     Elongated  un jointed  threads  rolled 
up  into  a  more  or  less  perfect  spiral:  frequently 
two  spirals  intertwine.     In  some  of  the  largest 
forms  a  vibratile  cilium  can  be  made  out  on 
each  end  of  the  thread. 

e.  Spirochsete.     Much  like  spirillum,   but  longer 
and  with  a  much  more  closely  rolled  spiral.     A 
very  actively  motile  but  not  common  form. 

7.  Examine  various  putrefying  fluids  for  Bacteria  and 
related  organisms. 

8.  Place  some  fresh-made  hay  infusion  in  three  flasks; 
boil  two  of  them  for  three  or  four  minutes,  and  while 
one  is  boiling  briskly  stop  its  neck  with  a  plug  of 
cotton-wool  and  continue  to  boil  for  a  minute  or 
two:  leave  the  necks  of  the  other  two  flasks  un- 
closed, and  put  all  three  away  in  a  warm  place. 

a.  In  a  day  or  two   abundant   Bacteria  will   be 
found  in  the  unboiled  flask. 

b.  In  the  boiled  but  unclosed  flask  Bacteria  will 
also  appear,  but  perhaps  not  quite  so  soon  as 
in  a. 

c.  In  the  flask  which  has  been  boiled  and  kept 
closed  Bacteria  will  not  appear,  if  the  experi- 
ment has  been  properly  performed,  even  if  it 
be  kept  for  many  months. 


V. 
MOULDS  (Penicillium  and  Mucor). 

Torula,  Protococcus  and  Amoeba  are  extremely  simple  con- 
ditions of  the  two  great  kinds  of  living  matter  which  are 
known  as  Plants  and  Animals.  No  plants  are  simpler  in 
structure  than  Torula  and  Protococcus,  and  the  only  ani- 
mals which  are  simpler  than  Amoeba,  are  essentially  Amoebae 
devoid  of  a  nucleus  and  contractile  vesicle.  Moreover,  how- 
ever complicated  in  structure  one  of  the  higher  plants  may 
be  in  its  adult  state,  when  it  commences  its  existence  it  is  as 
simple  as  Torula  or  Protococcus,  or  at  most  as  Torula  or  Pro- 
tococcus would  be  if  it  possessed  a  distinct  nucleus ;  and  the 
whole  plant  is  built  up  by  the  fissive  multiplication  of  the 
simple  cell  in  which  it  takes  its  origin,  and  by  the  subse- 
quent growth  and  metamorphosis  of  the  cells  thus  produced. 
The  like  is  true  of  all  the  higher  animals.  They  commence 
as  nucleated  cells,  essentially  similar  to  Amoebae  and  colour- 
less blood-corpuscles,  and  their  bodies  are  constructed  by 
aggregations  of  metamorphosed  cells,  produced  by  division 
from  the  primary  cell.  It  has  been  seen  that  Torula 
and  Protococcus,  similar  as  they  are  in  structure,  are  dis- 
tinguished by  certain  important  physiological  peculiarities  ; 
and  the  more  complicated  plants  are  divisible  into  two 
series,  one  produced  by  the  growth  and  modification  of  cells 
which  have  the  physiological  peculiarities  of  Torula  and 
contain  no  chlorophyll,  while  the  other,  and  far  larger,  series 


v.]  MOULDS.  31 

presents  chlorophyll,  and  has  the  physiological  peculiarities 
of  Protococcus.  The  former  series  comprises  the  Fungi,  the 
latter  all  other  plants ;  only  a  few  parasitic  forms  among 
these  being  devoid  of  chlorophyll. 

The  Fungi  take  their  origin  in  spores,  a  kind  of  cells, 
which,  however  much  they  may  vary  in  the  details  of  their 
structure,  are  essentially  similar  to  Torulce.  Indirectly  or 
directly,  the  spore  gives  rise  to  a  long  tubular  filament, 
which  is  termed  a  hyp  ha,  and  out  of  these  hyphae  the 
Fungus  is  built  up. 

One  of  the  commonest  Moulds,  the  Penidllium  glaucum, 
which  is  familiar  to  every  one  from  its  forming  sage-green 
crusts  upon  bread,  jam,  old  boots,  &c.  affords  an  excellent 
and  easily  studied  example  of  a  Fungus.  When  examined 
with  a  magnifying  glass,  the  green  appearance  is  seen  to  be 
due,  in  great  measure,  to  a  very  fine  powder  which  is  de- 
tached from  the  surface  of  the  mould  by  the  slightest  touch. 
Beneath  this  lies  a  felt-work  of  delicate  tubular  filaments, 
the  hyphae,  forming  a  crust  like  so  much  blotting-paper, 
which  is  the  mycelium.  From  the  free  surface  of  the  crust 
innumerable  hyphae  project  into  the  air  and  bear  the  green 
powder.  These  are  the  aerial  hyphce.  On  the  other  hand,  the 
attached  surface  gives  rise  to  a  like  multitude  of  longer 
branched  hyphae,  which  project  into  the  fluid  in  which  the 
crust  is  growing,  like  so  many  roots,  and  may  be  called  the 
submerged  hyphcz.  If  the  patch  of  Penidllium  has  but  a 
small  extent  relatively  to  the  surface  on  which  it  lies,  mul- 
titudes of  silvery  hyphae  will  be  seen  radiating  from  its 
periphery  and  giving  off  many  submerged,  but  few  or  no 
vertical,  or  subaerial,  branches.  Submitted  to  microscopic 
examination,  a  hypha  is  seen  to  be  composed  of  a  transpa- 
rent wall  (which  has  the  same  characters  as  the  cell-wall  of 
Torula)  and  protoplasmic  contents,  which  fill  the  tube 


3*  ELEMENTARY  BIOLOGY.  [CHAP. 

formed  by  the  wall,  and  present  large  central  clear  spaces, 
or  vacuoles.  At  intervals,  transverse  partitions,  continuous 
with  the  walls  of  the  tube,  divide  it  into  elongated  cells, 
each  of  which  contains  a .  correspondingly  elongated  proto- 
plasmic sac,  or  primordial  titride.  The  hyphae  frequently 
branch  dichotomously ;  and,  in  the  crust,  they  are  inex- 
tricably entangled  with  one  another ;  but  every  hypha,  with 
its  branches,  is  quite  distinct  from  every  other.  Those 
aerial  hyphse  which  are  nearest  the  periphery  of  the  crust 
end  in  simple  rounded  extremities ;  but  the  others  terminate 
in  brushes  of  short  branches,  and  each  of  these  branches,  as 
it  grows  and  elongates,  becomes  divided  by  transverse  con- 
strictions into  a  series  of  rounded  spores  arranged  like  a 
row  of  beads.  The  spores  formed  in  this  manner  are 
termed  conidia.  At  the  free  end  of  each  filament  of  the 
brush  the  conidia  become  very  loosely  adherent,  and  con- 
stitute the  green  powdery  matter  to  which  reference  has 
been  made.  Examined  separately,  a  conidium  is  seen  to  be 
a  spherical  body,  composed  of  a  transparent  sac,  enclosing 
a  minute  mass  of  protoplasm,  in  all  essential  respects  similar 
to  a  Tonda.  If  sown  in  an  appropriate  medium,  as  for 
example  Pasteur's  solution,  with  or  without  sugar,  the  coni- 
dium germinates.  Upon  from  one  to  four  points  of  its 
surface  an  elevation  or  bulging  of  the  cell-wall  and  of  its 
contained  protoplasm  appears.  This  rapidly  increases  in 
length,  and,  continually  growing  at  its  free  end,  gives  rise  to 
a  hypha,  so  that  the  young  Penicillium  assumes  the  form  of 
a  star,  each  ray  being  a  hypha.  The  hyphas  elongate,  while 
side  branches  are  developed  from  them  by  outgrowths  of 
their  walls ;  and  this  process  is  repeated  by  the  branches, 
until  the  hyphae  proceeding  from  a  single  conidium  may 
cover  a  wide  circular  area,  as  a  patch  of  mycelium.  When, 
as  is  usually  the  case,  many  conidia  germinate  close  together, 


V.]  MOULDS.  33 

their  hyphse  cross  one  another,  interlace,  and  give  rise 
to  a  papyraceous  crust.  After  the  hyphse  have  attained  a 
certain  length,  the  protoplasm  divides  at  intervals,  and 
transverse  septa  are  formed  between  the  masses  thus  divided 
off  from  one  another.  But  neither  in  this,  nor  in  any  other 
Fungus,  are  septa  formed  in  the  direction  of  the  length  of 
the  hypha. 

Very  early  in  the  course  of  the  development  of  the 
mycelium,  branches  of  the  hyphse  extend  downwards  into 
the  medium  on  which  the  mycelium  grows ;  while,  as  soon 
as  the  patch  has  attained  a  certain  size,  the  hyphas  in  its 
centre  give  off  vertical  aerial  branches,  and  the  develop- 
ment of  these  goes  on,  extending  from  the  centre  to  the 
periphery.  The  outgrowth  of  pencil-like  bunches  of  branches 
at  the  end  of  these  takes  place  in  the  same  order;  and 
these  branches,  becoming  transversely  cdnstricted  as  fast  as 
they  are  formed,  break  up  into  conidia,  which  are  ready  to 
go  through  the  same  course  of  development. 

The  conidia  may  be  kept  for  a  very  long  time  in  the  dry 
state,  without  their  readiness  to  germinate  being  in  any  way 
impaired,  and  their  extreme  minuteness  and  levity  enable 
them  to  be  dispersed  and  carried  about  by  the  slightest 
currents  of  air.  The  persistence  of  their  vitality  is  subject 
to  nearly  the  same  conditions  of  temperature  as  that  of 
yeast.  Not  unfrequently  Torula  make  their  appearance, 
in  abundance,  among  the  hyphae  and  conidia  of  Penitillium, 
and  appear  to  be  derived  from  them ;  but  it  is  still  a  disputed 
point,  whether  they  are  so  or  not. 

If  some  fresh  horse-dung  be  placed  in  a  jar  and  kept 
moderately  warm,  its  surface  will,  in  two  or  three  days,  be 
covered  with  white  cottony  filaments,  many  of  which  rise 
vertically  into  the  air,  and  end  in  rounded  heads,  so  that 
'<  M.  3 


34  ELEMENTARY  BIOLOGY.  [CHAP. 

they  somewhat  resemble  long  pins.  The  organism  thus 
produced  is  another  of  the  Fungi — the  mould  termed  Mucor 
mitsedo. 

Each  rounded  head  is  a  sporangium  ;  the  stalk  on  which 
it  is  supported  rises  from  one  of  the  filaments  which  ramify 
in  the  substance  of  the  horse-dung,  and  are  the  hyphce. 
Each  hypha  is,  as  in  Penicillium,  a  tube  provided  with  a 
tough  thickish  structureless  wall,  which  is  partly  composed 
of  cellulose,  and  is  filled  by  a  vacuolated  protoplasm.  In 
old  specimens,  transverse  partitions,  continuous  with  the 
walls  of  the  hyphae,  may  divide  them  into  chambers  or  cells. 
The  stalk  of  the  sporangium  is  a  hypha  of  the  same  structure 
as  the  others.  The  wall  of  the  sporangium  is  beset  with 
minute  asperities  composed  of  oxalate  of  lime,  and  it  con- 
tains a  great  number  of  minute  oval  bodies,  the  spores,  held 
together  by  a  transparent  intermediate  substance.  When  the 
sporangium  is  ripe,  the  slightest  pressure  causes  its  thin 
and  brittle  coat  to  give  way,  and  the  spores  are  separated 
by  the  expansion  of  the  intermediate  substance,  which 
readily  swells  up  and  finally  dissolves,  in  water.  The  greater 
part  of  the  wall  of  the  sporangium  then  disappears,  but  a 
little  collar,  representing  the  remains  of  its  basal  part, 
frequently  adheres  to  the  stalk.  The  cavity  of  the  stalk 
does  not  communicate  with  that  of  the  sporangium,  but  is 
separated  from  it  by  a  partition,  which  bulges  into  the 
cavity  of  the  sporangium,  forming  a  central  pillar  or  pro- 
jection. This  is  termed  the  columella  and  stands  con- 
spicuously above  the  collar,  when  the  sporangium  has  burst 
and  the  spores  are  evacuated. 

The  spores  are  oval  and  consist  of  a  sac.  having  the 
same  composition  as  the  wall  of  the  hypha,  which  encloses 
a  mass  of  protoplasm.  When  they  are  sown  in  an  appro- 
priate medium,  as  for  example  in  Pasteur's  solution,  they 


v.]  MOULDS.  35 

enlarge,  become  spheroidal,  and  then  send  out  several 
thick  prolongations.  Each  of  these  elongates,  by  constant 
growth  at  its  free  end,  and  becomes  a  hypha,  from  which 
branches  are  given  off,  which  grow  and  ramify  in  the  same 
way.  As  all  the  ramifying  hyphae  proceed  from  the  spore 
as  a  centre,  their  development  gives  rise,  as  in  Penicillium, 
to  a  delicate  stellate  mycelium.  At  first,  no  septa  are  deve- 
loped in  the  hyphae,  so  that  the  whole  mycelium  may  be 
regarded  as  a  single  cell  with  long  and  ramified  processes, 
and  the  Mucor,  at  this  stage,  is  an  unicellular  organism. 
From  near  the  centre  of  the  mycelium  a  branch  is  given  off 
from  a  hypha,  rises  vertically,  and  after  attaining  a  certain 
length  ceases  to  elongate.  Its  free  end  dilates  into  a 
rounded  head,  which  gradually  increases  in  size,  until  it 
attains  the  dimensions  of  a  full-grown  sporangium;  and,  at 
the  same  time,  the  protoplasm  contained  in  this  head 
becomes  separated  from  that  in  the  stalk  by  a  septum, 
which  is  curved  towards  the  cavity  of  the  sporangium,  and 
constitutes  the  columella.  The  wall  of  the  sporangium, 
thus  formed,  becomes  covered  externally  with  a  coat  of 
oxalate  of  lime  spines.  As  the  sporangium  increases  in 
size,  its  protoplasmic  contents  become  marked  out  into  a 
large  number  of  small  oval  masses,  which  are  close  together, 
but  not  in  actual  contact.  Each  of  these  masses  next 
becomes  completely  separate  from  the  rest,  surrounds  itself 
with  a  cellulose  coat,  and  becomes  a  spore;  while  the 
protoplasm  not  thus  used  up  in  the  formation  of  spores, 
appears  to  give  rise  to  the  gelatinous  intermediate  sub- 
stance, which  swells  up  in  water,  referred  to  above.  The 
walls  of  the  spores  become  coloured,  and  that  of  the  spo- 
rangium gradually  thins,  until  it  is  reduced  to  little  more 
than  the  outer  crust  of  oxalate  of  lime.  The  sporangium 
now  readily  bursts,  and  the  spores  are  separated  by  the 

3—2 


3  6  ELEMENTARY  BIOLOGY.  [CHAP. 

swelling  and  eventual  dissolution  of  the  gelatinous  interme- 
diate matter.  Sporangia,  in  which  spores  are  produced  by 
division  of  the  protaplasm,  are  commonly  termed  asci,  and 
the  spores  receive  the  name  of  ascospores. 

There  appears  to  be  no  limit  to  the  extent  to  which  the 
Mucor  may  be  reproduced  by  this  process  of  asexual  deve- 
lopment of  spores,  by  the  fission  of  the  contents  of  the 
sporangium;  nor  does  any  other  mode  of  multiplication 
become  apparent,  so  long  as  the  mould  grows  in  a  fluid 
medium  and  is  abundantly  supplied  with  nourishment. 

But  when  growing  in  nature,  in  such  matters  as  horse- 
dung,  a  method  of  reproduction  is  set  up  which  represents 
the  sexual  process  in  its  simplest  form.  Adjacent  hyphae, 
or  parts  of  the  same  hypha,  give  off  short  branches,  which 
become  dilated  at  their  free  ends,  and  approach  one  ano- 
ther, until  these  ends  are  applied  together.  The  proto- 
plasm in  each  of  the  dilated  ends  becomes  separated  by  a 
septum  from  that  of  the  rest  of  the  branch;  the  two  cells 
thus  formed  open  into  one  another  by  their  applied  faces, 
and  their  protoplasmic  contents  becoming  mixed  together, 
form  one  spheroidal  mass,  to  the  shape  of  which  the  coa- 
lesced cell-membranes  adapt  themselves.  This  process  of 
conjugation  evidently  represents  that  of  sexual  impregnation 
among  higher  organisms,  but  as  there  is  no  morphological 
difference  between  the  modified  hyphae  which  enter  into 
relation  with  one  another,  it  is  impossible  to  say  which 
represents  the  male,  and  which  the  female,  element.  The 
product  of  conjugation  is  termed  a  zygospore.  Its  cellulose 
coat  becomes  separated  into  an  outer  layer  of  a  dark  black- 
ish hue,  the  exosporium,  and  an  inner  colourless  layer,  the 
endosporium.  The  outer  coat  is  raised  into  irregular  eleva- 
tions, to  which  corresponding  elevations  of  the  inner  coat 
correspond. 


v.]  MOULDS.  37 

Placed  in  favourable  circumstances,  the  zygospore  does 
not  immediately  germinate;  but,  after  a  longer  or  shorter 
period  of  rest,  the  exosporium  and  the  endosporium  burst, 
and  a  bud-like  process  is  thrown  out,  which,  usually,  grows 
only  into  a  very  short  unbranched  hypha.  From  this  hypha 
a  vertical  prolongation  is  developed,  which  becomes  con- 
verted into  a  sporangium,  such  as  that  already  described, 
whence  spores  are  produced,  which  give  rise  to  the  ordinary 
stellate  mycelium.  Thus,  Mucor  presents  what  is  termed  an 
"alternation  of  generations"  The  zygospore  resulting  from 
a  sexual  process  developes  into  a  rudimentary  mycelium, 
with  a  single  sporangium  which  constitutes  the  first  gene- 
ration (A).  This  gives  rise,  by  the  asexual  development  of 
spores  in  its  sporangium,  to  the  second  generation  (£), 
represented  by  as  many  separate  Mucores  as  there  are 
spores.  The  second  generation  (J3)  may  give  rise  sexually 
to  zygospores  and  so  reproduce  the  generation  (A)-,  but, 
more  usually,  an  indefinite  series  of  generations  similar  to 
(J3)  are  produced  from  one  another  asexually,  before  (A) 
returns. 

When  Mucor  is  allowed  to  grow  freely  at  the  surface  of 
a  saccharine  liquid,  it  takes  on  no  other  form  than  that 
described;  but,  if  it  be  submerged  in  the  same  liquid,  the 
mode  of  development  of  the  younger  hyphae  becomes 
changed.  They  break  up,  by  a  process  of  constriction, 
into  short  lengths,  which  separate,  acquire  rounded  forms, 
and  at  the  same  time  multiply  by  budding  after  the  manner 
of  Torulcz.  Coincidentally  with  these  changes,  an  active 
fermentation  is  excited  in  the  fluid,  so  that  this  "  Mucor- 
Torula"  functionally  as  well  as  morphologically,  deserves 
the  name  of '  yeast.' 

If  the  Mucor-Torula  is  filtered  off  from  the  saccharine 
solution,  washed,  and  left  to  itself  in  moist  air,  the  Torulce 


38  ELEMENTARY  BIOLOGY.  [CHAP. 

give  off  very  short  aerial  hyphae,  which  terminate  in  minute 
sporangia.  In  these  a  very  small  number  of  ordinary 
mucor  spores  is  developed,  but,  in  essential  structure,  both 
the  sporangia  and  the  spores  resemble  those  of  normal 
Mucor. 

LABORATORY  WORK. 
A.     PENICILLIUM. 

Prepare  some  Pasteur's  fluid,  and  leave  it  exposed  to 
the  air  in  saucers  in  a  warm  place ;  if  Penicillium  spores  are 
at  hand  add  a  few  to  the  fluid  in  each  saucer :  if  spores 
cannot  be  obtained,  the  fluid,  if  simply  left  to  itself,  will 
probably  be  covered  with  Penicillium  in  ten  days  or  a 
fortnight.  Sometimes,  however,  the  fluid  will  overrun  with 
Bacteria,  to  the  exclusion  of  everything  else.  And  very 
frequently  other  moulds,  such  as  Aspergillus,  or  Mucor, 
may  appear  instead  of  or  along  with  Penicillium. 

1.  NAKED-EYE  CHARACTERS.    Note  the  powdery-looking 
upper    surface,    white    in    young    specimens,    pale 
greenish  in  older,  and  later  still  becoming  dark  sage- 
green:  the   smooth  pale  under  surface:  the  dense 
tough  character  of  the  mycelium. 

2.  HlSTOLOGICAL  STRUCTURE. 

a.    The  mycelium, 

a.      Tease  a  bit  out  in  water,  and  examine  first  with 

low,  and  then  with  a  high  power  :  it  is  chiefly 

made  up  of  interlaced  threads  or  tubes — the 

a.      Hyphcz.      Note   their  diameter  (measure) — 

form — subdivisions  (cells] — dichotomous  mode 

of  branching — and  structure:    the   external 


v.]  MOULDS.  39 

homogeneous  sac;   the  granular  less   trans- 
parent protoplasm ;  the  small  round  vacuoles. 
Draw. 
/?.      The  intermixed  Torulce.     Note  their  size  and 

number. 

b.  Hold  a  bit  of  the  mycelium  between  two  pieces 
of  carrot,  and  cut  a  thin  vertical  section  with  a 
sharp  razor  :  mount  in  water  and  examine  with 
low  and  high  power. 

b.  The  submerged  hyphse. 

Small  branched  threads  hanging  down  from  the  under 
surface  of  the  mycelium :  repeat  the  observations 
2.  a.  a>  «• 

c.  The  aerial  hypliss  and  conidiophores. 

Tease  out  in  water  a  bit  from  the  surface  of  one  of 
the  greenish  patches;  observe  the  difficulty  with 
which  water  wets  it.  Examine  with  low  and  high 
power. 

Note  ;— 

a.     The  primary  erect  hypha. 

/?.    Its  division  into  a  number  of  branches. 

y.     The  division  of  the  terminal  branches  by  con- 
strictions into  a  chain  of  conidia.     Draw. 

d.  The  conidia. 

a.  Their  Size  (measure). 

Form;  spherical. 

Structure;  sac,  protoplasm,  vacuole. 

b.  Stain  with  magenta  and  iodine. 

c.  Treat  another  specimen  with  potash. 


40  ELEMENTARY  BIOLOGY.  [CHAP. 

e.     The  germination  of  the  Conidia,  and  building  up 
of  the  Mycelium. 

a.  Sow  some  conidia  in  Pasteur's  fluid  in  a  watch-glass  ; 
protect  from  evaporation,  and  watch  the  development 
of  the  mycelium  (examine  the  surface  with   a  low 
power) ;  then  the  formation  of  aerial  hyphae ;  finally 
the  production  of  new  conidia. 

b.  [Sow  Conidia  in  Pasteur's  fluid  in  a  moist  chamber,  and 
watch  from  day  to  day ;  note  the  formation  of  eminences 
at  one  or  more  points  on  a  conidium ;  the  elongation  of 
these  eminences  to  form  hyphae ;   the  branching  and 
interlacement  of  the  hyphae.] 

B.       MUCOR   MUCEDO. 

1.  Place  some  fresh  horse-dung  under  a  bell-jar  and 
keep  moist  and  warm;  in  from  24  to  48  hours  its 
surface  will  nearly  always  be  covered  by  a  crop  of 
erect  aerial  mucor-hyphae,  each  ending  in  a  minute 
enlargement  (sporangium)  just  visible  with  the  un- 
assisted eye :  it  is  this  first  crop  of  hyphae  and  spor- 
anges  which  is  to  be  examined. 

2.  Snip  off  a  few  of  the  hyphae  with  a  pair  of  scissors, 
mount  in  water,  and  examine  with  i  inch  obj. 

a.     Large  unbranched   hyphae,  each   ending   in   a 
spherical  enlargement  (sporangium). 

3.  Examine  with  ^  obj. 
a.    The  hyphae. 

a.  Their  size;  they  greatly  exceed  the  hyphae  of 
Penidllium  both  in  length  and  diameter. 

ft.  Their  structure ;  homogeneous  sac,  granular 
protoplasm,  vacuoles :  septa  absent  except 
close  to  the  sporange. 


v.]  MOULDS.  41 

y.  Treat  with  iodine  and  magenta;  the  proto- 
plasm is  stained. 

8.  Treat  another  specimen  with  Schulz's  solu- 
tion ;  the  wall  is  stained  violet. 

b.  The  sporangia  or  asci. 
Examine  with  -|  obj. 

a.  Their  size  and  form. 

b.  Their  structure. 

a.  The  homogeneous  enveloping  sac  covered  by 
irregular  masses  of  calcic  oxalate. 

/?.  The  granular  protoplasmic  contents :  un- 
segmented  in  some;  divided  into  a  great 
number  of  distinct  oval  masses  (ascospores}  in 
others. 

y.  The  projection  into  the  sporangial  cavity  of 
the  convex  septum  (columelld)  which  separates 
the  hypha  from  the  sporange. 

8.  The  collar  projecting  around  the  base  of  the 
columella  of  burst  sporangia. 

c.  Stain  some   with  iodine;   others  with  Schulz's 
solution. 

c.  The  ascospores. 

a.      Crush  some  ripe  asci  by  gentle  pressure  upon 

the  cover-glass.     Examine  with  \  obj. 
a.      The  size  of  the  ascospores  (measure), 
p.     Their  form ;  cylindrical  and  elongated. 
y.      Their  structure. 
8.      Stain  with  iodine  and  magenta. 


VI. 

STONEWORTS  (Chara  and  Nitella). 

THESE  water-weeds  are  not  uncommonly  found  in  ponds 
and  rivers,  growing  in  tangled  masses  of  a  dull  green  colour. 
Each  plant  is  hardly  thicker  than  a  stout  needle,  but  may 
attain  a  length  of  three  or  four  feet.  One  end  of  the  stem 
is  fixed  in  the  mud  at  the  bottom,  by  slender  thread-like 
roots,  the  other  floats  at  the  surface.  At  intervals,  append- 
ages, consisting  of  leaves,  branches,  root-filaments,  and  repro- 
ductive organs,  are  disposed  in  circles,  or  whorls.  In  the 
middle  and  lower  parts  of  the  plant  these  whorls  are  dis- 
posed at  considerable  and  nearly  equal  distances;  but, 
towards  the  free  upper  end,  the  intervals  between  the  whorls 
dimmish,  and  the  whorled  appendages  themselves  become 
shorter,  until,  at  the  very  summit,  they  are  all  crowded 
together  into  a  terminal  bud,  which  requires  the  aid  of  the 
microscope  for  its  analysis. 

The  parts  of  the  stem,  or  axis,  from  which  the  append- 
ages spring  are  termed  nodes;  the  intervening  parts  being 
internodes.  When  viewed  with  a  hand-magnifier  the  inter- 
nodes  exhibit  a  spiral  striation. 

In  Chara,  each  internode  consists  of  a  single,  much- 
elongated  cell,  which  extends  throughout  its  whole  length, 
invested  by  a  cortical  layer,  composed  of  many  cells,  the 
spiral  arrangement  of  which  gives  rise  to  the  superficial 
marking  which  has  been  noted.  And  this  multicellular 
structure  is  continued  from  the  cortical  layer,  across  the 


vi.]  STONE  WORTS.  43 

stem,  at  each  node.  The  stem  therefore  consists  of  a  series 
of  long,  axial  cells,  contained  in  as  many  closed  chambers 
formed  by  the  small  cortical  cells.  The  nodes  are  the  mul- 
ticellular  partitions  between  these  chambers.  The  branches 
are  altogether  similar  in  structure  to  the  main  stem.  The 
leaves  are  also  similar  to  the  stem,  so  far  as  they  consist  of 
axial  and  cortical  cells,  but  they  differ  in  the  form  and 
proportions  of  these  cells,  as  well  as  in  the  fact  that  the 
summit,  or  free  end,  of  the  leaf  is  always  a  much-elongated 
pointed  cell.  The  branches  spring  from  the  re-entering 
angle  between  the  stem  and  the  leaf,  which  is  termed  the 
axilla  of  the  leaf;  and,  in  the  same  position,  at  the  fruiting 
season  of  the  plant  are  found  the  reproductive  organs. 
These  are  of  two  kinds,  the  one  large  and  oval,  the  sporangia 
or  spore-fruits,  the  other  smaller  and  globular,  the  antheridia. 
Both,  when  ripe,  have  an  orange-red  colour,  and  are  seated 
upon  a  short  stalk. 

If  a  growing  plant  be  watched,  it  will  be  found  that  it 
constantly  increases  in  length  two  ways.  New  nodes,  inter- 
nodes,  and  whorls  of  appendages  are  constantly  becoming 
obvious  at  the  base  of  the  terminal  bud ;  and  these  append- 
ages increase  in  size  and  become  more  and  more  widely 
separated,  until  they  are  as  large  and  as  far  apart  as  in  the 
oldest  parts  of  the  plant.  The  appendages  at  first  consist 
exclusively  of  leaves  and  root-filaments  (rhizoids\  and  it  is 
only  when  these  have  attained  their  full  size,  that  branches, 
spore-fruits  and  antheridia  are  developed  in  their  axillae. 
Sometimes  rounded  cellular  masses  appear  in  the  axillae  of 
the  leaves,  and,  becoming  detached,  grow  into  new  plants. 
These  are  comparable  to  the  bulbs  of  higher  plants. 

If  the  innermost  part  of  the  terminal  bud,  which  con- 
stitutes the  free  end  of  the  axis,  or  stem,  be  examined,  it 
will  be  found  to  be  formed  by  a  single  nucleated  cell, 


44  ELEMENTARY  BIOLOGY.  [CHAP. 

separated  by  a  transverse  septum  from  another.  Beneath 
this  last  follows  another  cell,  which  has  already  undergone 
division  into  several  smaller  cells  by  the  development  of 
longitudinal  septa.  This  is  the  most  newly- formed  node. 
Below  this  again  is  a  single  cell,  which  is  both  longer  and 
broader  than  those  at  the  apex,  and  is  an  internodal  cell. 
Below  it  follows  another  node,  composed  of  more  numerous 
small  cells  than  in  the  first.  Some  of  the  peripheral  cells 
of  this  node  are  undergoing  growth  and  division,  and  thus 
give  rise  to  cellular  prominences,  which  are  rudiments  of 
the  first  whorl  of  leaves.  In  the  still  lower  parts  of  the 
stem  the  internodal  cells  get  longer  and  longer,  but  they 
never  divide.  The  nodal  cells,  on  the  other  hand,  multiply 
by  division,  but  do  not  greatly  elongate.  From  the  first, 
the  nodal  cells  overlap  the  internodal  cell,  so  as  to  meet 
round  its  equator,  and  thus  completely  invest  it  externally. 
And,  as  the  internodal  cell  grows  and  elongates,  the  overlap- 
ping parts  of  the  nodes  increase  in  length  and  become  divided 
into  internodal  and  nodal  cells,  which  take  on  a  spiral 
arrangement,  and  thus  give  rise  to  the  cortical  layer. 

Thus  the  whole  plant  is  composed  of  an  aggregation  of 
simple  cells;  and,  while  it  lives,  new  nodes  and  internodes 
are  continually  being  added  at  its  summit,  or  growing  point. 
The  internodal  cells  which  give  rise  to  the  centre  of  the 
stem  undergo  no  important  change,  except  great  increase 
of  size,  after  they  are  once  formed.  The  nodal  cells,  on 
the  contrary,  undergo  division  with  comparatively  little  in- 
crease in  size.  And  out  of  them,  the  nodes,  the  cortical 
layer,  and  all  the  appendages,  are  developed. 

In  all  the  young  cells  of  Chara  a  nucleus  of  relatively 
large  size  is  to  be  seen  imbedded  in  the  centre  of  the  pro- 
toplasm, which  is  motionless,  and  is  enclosed  in  a  structure- 
less cell-wall,  containing  cellulose.  As  the  cell  grows 


vi.]  STONE  IVOR  TS.  45 

larger,  the  centre  of  the  protoplasm  becomes  occupied  by  a 
watery  fluid,  and  its  thick  periphery,  which  remains  applied 
against  the  cell-wall,  constitutes  the  wall  of  a  sac,  or  pri- 
mordial utricle,  in  which  the  nucleus  is  imbedded.  In  the 
larger  cells  the  primordial  utricle  is  readily  detached  and 
made  to  shrivel  up  into  the  middle  of  the  cell  by  treatment 
with  strong  alcohol. 

Numerous  small  green  bodies — chlorophyll  grains — are 
imbedded  in  the  outer,  or  superficial,  part  of  the  primordial 
utricle.  And  they  increase  in  number  by  division,  as  the 
cell  enlarges.  These  chlorophyll  grains  are  composed  of 
protoplasmic  matter,  which  frequently  contains  starch  gra- 
nules, and  is  impregnated  with  the  green  colouring  sub- 
stance. 

During  life,  the  layer  of  the  primordial  utricle  which 
lies  next  to  the  watery  contents  of  all  the  larger  cells  is  in 
a  state  of  incessant  rotatory  motion,  while  the  outermost 
layer  which  contains  the  chlorophyll  grains  is  quite  still. 
In  the  large  cells,  so  long  as  the  nucleus  is  discernible,  it  is 
carried  round  with  the  rotating  stream. 

The  antheridium  is  a  globular  spheroidal  body  with  a 
thick  wall,  made  up  of  eight  pieces,  which  are  united  by 
interlocking  edges.  The  four  pieces  which  make  up  the 
hemisphere  to  which  the  stalk  of  the  antheridium  is  at- 
tached, are  foursided,  the  other  four  are  triangular.  From 
the  centre  of  the  inner,  concave  face  of  each  piece  a  sort  of 
short  process,  the  handle  or  manubriumy  projects  into  the 
cavity  of  the  hollow  sphere.  At  the  free  end  of  the  manu- 
brium  is  a  rounded  body,  the  capitulum,  which  bears  six 
smaller,  secondary  capitnla;  and  each  secondary  capitulum 
gives  attachment  to  four  long  filaments  divided  by  trans- 
verse partitions  into  a  multitude  (100  to  200)  of  small 
chambers.  Thus,  there  may  be  as  many  as  20,000  to 


46  ELEMENTARY  BIOLOGY.  [CHAP. 

40,000  chambers  in  each  antheridium  (8  x  6  x  4  x  100  or 
x  200).  The  several  pieces  of  which  the  wall  of  the  an- 
theridium is  composed,  the  manubrium,  the  capitula,  the 
secondary  capitula  and  the  chambers  of  the  filaments,  are 
all  more  or  less  modified  cells,  as  may  be  proved  by  tracing 
the  antheridia  from  their  earliest  condition,  as  small  pro- 
cesses of  the  nodal  region,  to  their  complete  form.  The 
cells  of  the  filaments  are,  at  first,  like  any  other  cells;  but, 
by  degrees,  the  protoplasm  of  each  becomes  changed  into  a 
thread-like  body,  thicker  at  one  end  than  at  the  other,  and 
coiled  spirally  like  a  corkscrew.  From  the  thin  end  two 
long  cilia  proceed ;  and,  when  the  cells  are  burst,  and  the 
antherozooids  are  set  free,  they  are  propelled  rapidly,  with 
the  small  end  forwards,  by  the  vibration  of  the  cilia.  These 
antherozooids  answer  to  the  spermatozoa  of  animals,  and 
represent  the  male  element  of  the  Chara. 

The  sporangia  or  spore-fruits  are  borne  upon  short  stalks, 
the  end  of  which  supports  a  large  oval  central  cell;  five 
spirally-disposed  sets  of  cells  invest  this,  an  aperture  being 
left  between  the  investing  cells  at  the  apex  of  the  sporan- 
gium. When  the  antheridia  attain  maturity  they  burst,  the 
antherozooids  are  set  free,  and  swarm  about  in  the  water. 
Some  of  them  enter  the  aperture  of  the  sporangium,  and,  in 
all  probability,  pierce  the  free  summit  of  the  oval  central  cell, 
and  enter  its  protoplasm ;  but  all  the  steps  of  this  process 
of  impregnation  have  not  been  worked  out.  The  result, 
however,  is,  that  the  contents  of  the  central  cell  become 
full  of  starchy  and  oily  matter;  the  spiral  cells  forming  its 
coat  acquire  a  dark  colour  and  hard  texture,  and  the  spo- 
rangium, detaching  itself,  falls  into  the  mud. 

After  a  time  it  germinates;  a  tubular  process,  like  a 
hypha,  protrudes  from  its  open  end,  and  almost  immediately 
gives  off  a  branch,  which  is  the  first  root  (compare  the  ger- 


vi.]  STONEWORTS.  47 

mination  of  the  spore  of  a  fern  below).  The  hypha-like 
tube  elongates,  and  becomes  divided  transversely  into  cells, 
the  protoplasm  of  which  developes  chlorophyll.  Very  soon, 
the  further  growth  of  this  pro-embryo  is  arrested.  But  one 
of  the  cells,  which  lies  at  some  distance  below  the  free  end 
of  the  pro-embryo,  undergoes  budding,  and  gives  rise  to  a 
set  of  leaves  (which  are  not  arranged  in  a  whorl),  amidst 
which  a  bud  appears,  which  has  the  structure  of  the  termi- 
nal bud  of  the  adult  Chara  stem,  and  grows  up  into  a  new 
Chara, 

We  have  then,  in  Chara,  a  plant  which  is  acrogenous  (or 
grows  at  its  summit),  and  which  becomes  segmented  by  the 
development  of  appendages,  at  intervals,  along  an  axis; 
which  multiplies,  asexually  by  bulb-like  buds,  and  also  mul- 
tiplies sexually  by  means  of  the  antherozooids  (male  ele- 
ments) and  central  cells  of  the  sporangia  (female  elements) ; 
in  which  the  first  product  of  the  germination  of  the  impreg- 
nated ovicell  is  a  hypha-like  body,  from  which  the  young 
Chara  is  developed  by  the  germination  and  growth  of  one 
cell;  so  that  there  is  a  sort  of  alternation  of  generations, 
though  the  alternating  forms  are  not  absolutely  distinct 
from  one  another. 

Chara  flourishes  in  pond-water  under  the  influence  of 
sunlight,  and  by  the  aid  of  its  chlorophyll,  so  that  its  nutri- 
tive processes  must  be  the  same  as  those  of  Protococcus. 
From  its  complete  immersion,  and  the  absence  of  any  duct- 
like,  or  vascular  tissues,  it  is  probable  that  all  parts  absorb 
and  assimilate  the  nutriment  contained  in  the  water ;  and 
that,  except  so  far  as  the  reproductive  organs  are  concerned, 
there  is  a  morphological  differentiation  of  organs,  unaccom- 
panied by  a  corresponding  physiological  differentiation. 

Nitetta  is  a  rarer  plant  than  Chara,  and  is  simpler  in 
structure,  its  axis  being  devoid  of  the  cortical  layer.  In 


48  ELEMENTARY  BIOLOGY.  [CHAP. 

other  respects,  however,  it  is  very  similar  to  Chara,  and  its 
structure  is  more  easily  made  out. 

[The  Characea,  or  plants  belonging  to  the  genera  Chara  and 
Nitella,  are  found  in  all  parts  of  the  world,  and  are  in  many 
respects  closely  allied  to  the  Alga,  or  water- weeds.  But  no 
Alga  are  provided  with  an  axis  and  appendages  possessing  a 
similar  structure,  or  following  the  same  law  of  growth,  nor 
have  any  similar  reproductive  organs.  The  antherozooids  of 
the  Characece  are,  in  fact,  similar  to  those  of  the  mosses,  from 
which  however  the  Characea  differ  widely  in  all  other  respects.] 


LABORATORY  WORK. 

A.  NAKED-EYE  CHARACTERS. 

Note  the  slender  elongated  axis  (stem}')  the  whorled 
appendages  (leaves] ;  the  nodes  and  internodes;  the  shortening 
of  the  latter  towards  the  apex  of  the  stem;  the  rhizoids. 

a.  The  roots;  small;  serving  chiefly  for  attachment, 
the  plant  getting  most  of  its  nutrition,  through 
other  parts,  from  matters  dissolved  in  the  water. 

b.  The  leaves;   their  sub-divisions   (leaflets) ;   their 
form,  size,  &c. 

c.  The  spore-fruits  and  anther idia;   their  position, 
size,  form,  colour. 

Draw  a  portion  including  two  or  three  internodes. 

B.  HlSTOLOGICAL   STRUCTURE. 

a.    The  stem. 

i.  Examine  the  outside  of  a  fresh  internode  with  a  low 
power,  or  pocket  lens,  to  see  the  spirally-arranged 
cortical  cells. 


vi.]  STONEWORTS.  49 

2.  Hold  a  bit  of  fresh  stem  between  two  pieces  of  carrot, 
or  imbed  it  in  paraffin,  and,  with  a  sharp  razor,  cut 
thin  transverse  and  longitudinal  slices  through  nodes 
and  internodes.     Note  the  cavity  of  the  large  central 
cell  (medullary  or  internodal  cell)  in  the  internodes ; 
the  cortical  cells ;  round  the  medullary  cell;  the  nodal 
cells,  and  the  interruption  of  the  central  cavity  at  the 
nodes. 

3.  Examine  similar  sections  in  specimens  treated  with 
spirit,  and  also  preparations  made  by  teasing  or  press- 
ing out  in  glycerine  bits  of  stem  from  chromic  acid 
(0-2  per  cent.)  preparations :  make  out  in  these, — 

a.      The  nodal,  internodal,  and  cortical  cells. 

/3.  The  wall  (sac),  protoplasmic  layer  (primordial 
utricle),  nucleus,  and  vacuole  of  each  cell.  (The 
nucleus  is  not  always  to  be  found  in  old  cells.) 

4.  Examine  sections  from  the  fresh  stem  to  make  out 
the  points  detailed  in  B.  a.  3.  (3.     The  protoplasm 
and  nucleus  are  difficult  to  see.     Note  the  chloro- 
phyll-granules.    (See  B.  b.  y.) 

5.  Stain  sections  of  the  fresh  stem  with  iodine,  and 
magenta:   note  the  results. 

b.     The  leaves. 

Examine  fresh  and  chromic  acid  specimens, 

a.      The  large  uncovered  terminal  cell. 
(3.     Then  a  series  of  internodal  cells,  separated 
from  one  another,  and  covered-in,  by  nodal 
cells :  the  sac,  protoplasm,  nucleus,  and  vacuole 
of  each. 

y.      The  chlorophyll:  collected  into  oval  granules, 
and   arranged   so  as  to  leave  an  oblique 
M,  4 


5o  ELEMENTARY  BIOLOGY.  [CHAP. 

uncoloured  band  round  each  cell;  the  position 
of  these   granules,  in  the   more   superficial 
layer  of  the  protoplasm. 
8.      The  protoplasmic  movements  (see  C.  a.). 
c.    The  terminal  bud. 

Dissect  out  chromic  acid  specimens  as  far  as  pos- 
sible with  needles,  and  then  press  gently  out  in 
glycerine.     Note  in  different  specimens — 
a.      The  terminal  or  apical  cell: 

a.      Its  form:  hemispherical,  the  rounded  surface 
free;  the  flat  surface  attached  to  the  cell  below 
it. 
ft.     Structure:  sac,  protoplasm,  nucleus ;  no  vacuole 

present. 

y.     Sometimes  two  nuclei;  preliminary  to  division. 
S,      Its  mode  of  division;   across  the  long  axis  of 
the  stem,  giving  rise   to   two  superimposed 
nucleated  cells. 

/>.  The  further  fate  of  the  new  cells  which  are 
successively  segmented  off  from  the  terminal 
cell;  work  back  in  your  specimens  from  the 
terminal  cell. 

a.  The  new  cells  are  successively  nodal  &&&  inter- 
nodal;  the  latter  enlarge,  develope  a  large 
vacuole,  and  ultimately  form  the  medullary 
cells  of  the  internodes ;  they  never  divide. 
/?.  The  nodal  cells  divide  freely,  and  do  not 
increase  much  in  size;  they  give  origin  to  the 
nodes  and  the  cortical  cells. 

c.       The  development  of  leaves:  by  the  multiplication 
and  outgrowth  of  nodal  cells. 


vi.]  STONEWORTS.  51 

d.  Their  growth  at  the  base,   the  terminal  leaf-cell 
soon  attaining  its  full  size  and  not  dividing. 

e.  The  development  of  branches;  from  nodal  cells 
in  leaf-axils,  which  take  on  the  character  of  ter- 
minal cells. 

d.  The  spore-fruits. 

Examine  fresh,  under  a  low  power. 

a.  Made  up  externally  of  five  twisted  cells,  bearing 
at  their  apices  five  smaller,  not  twisted  cells. 

/?.  Cut  sections  from  imbedded  specimens,  and 
examine  with  a  high  power:  make  out  the 
large  central  nucleated  cell;  the  fatty  and 
starchy  matters  contained  in  it;  stain  with 
iodine. 

y.  Press  out  chromic  acid  specimens  in  glycerine ; 
make  out  the  above  points  (d.  a,  /3). 

8.  Examine  chromic  acid  specimens  for  young 
spore-fruits,  and  press  them  out  in  glycerine : 
make  out  in  the  youngest  the  five  roundish 
cells  surrounding  a  central  one;  then  in  older 
specimens  the  elongation,  and  twisting  of  the 
external  cells,  and  the  separation  of  their  apices 
as  five  distinct  cells. 

e.  The  antheridia. 

a.      Examine,  with  a  low  power,   a  ripe   (orange- 
coloured)  one. 

a.      Make  out  its  external  dentated  cells. 
/?.     Tease  out  a  ripe  antheridium  in  water;  and 
examine  with  a  high  power;  note  the  flat, 
dentated,  nucleated  external  cells ;  the  cylin- 
drical cell  (manubrium)  springing  perpendicu- 

4—2 


5?  ELEMENTARY  BIOLOGY.  [CHAP. 

larly  from  the  inner  surface  of  each;  the 
roundish  cell  (capituhuri)  on  the  inner  end  of 
the  manubrium;  the  six  secondary  capitula 
attached  to  the  capitulum  ;  the  thread-like 
filaments  (usually  four)  proceeding  from  each 
of  the  secondary  capitula. 

y.  The  structure  of  these  threads;  each  consists 
of  a  single  row  of  cells,  containing  in  unripe 
specimens  nucleated  protoplasm;  in  older 
specimens  each  contains  a  coiled-up  anthero- 
zooid. 
b.  The  antherozooids. 

a.  Their  form  and  structure ;  thickened  at  one 
end  and  granular;  tapering  off  gradually  to- 
wards the  other  end,  which  is  hyaline  and 
has  two  long  cilia  attached  to  it. 
/3.  The  movements  in  water  of  ripe  anthero- 
zooids. 

[Sometimes  Chara  cannot  be  obtained,  when  Ni- 
tella,  another  genus  of  the  same  Natural  Order,  and 
of  similar  habit  and  structure,  can.  Nearly  all  the 
points  above  described  for  Chara  can  be  made  out  in 
Nitella,  with  the  following  differences:  the  cortical 
cells  of  the  stem  and  leaves  are  absent,  and,  in  the 
commoner  species,  the  plant  is  not  hardened  by  cal- 
careous deposit ;  the  branches  arise,  not  one  from  a 
whorl  of  leaves,  but  two;  and  the  five  twisted  cells  of 
the  spore-fruit  are  each  capped  by  two  small  cells, 
instead  of  one.] 

G.     PROTOPLASMIC  MOVEMENTS  IN  VEGETABLE  CELLS. 

a.  Chara.  Take  a  vigorous-looking  fresh  Chara  or 
Nitella  cell  (say  the  terminal  cell  of  a  leaf),  and 
examine  it  in  water  with  a  high  power.  Note 


vi.]  STONEWORTS.  53 

the  superficial  layer  of  protoplasm  in  which  the 
chlorophyll  lies;  it  is  stationary:  focus  through 
this  layer  and  examine  the  deeper  one;  note 
the  currents  in  it,  marked  by  the  granules  they 
carry  along:  their  direction;  in  the  long  axis 
of  the  cell,  up  one  side  and  down  the  other, 
the  boundary  of  the  two  currents  being  marked 
by  the  colourless  band,  in  which  no  movements 
occur.  Try  to  find  the  nucleus ;  it  has  usually 
disappeared  in  cells  in  which  currents  have 
commenced,  but  when  present  is  passive  and 
carried  along  by  them.  Sometimes  it  is  very 
difficult,  on  account  of  the  incrustation  of  the 
leaf-cells  of  Chara,  to  make  out  the  protoplasmic 
movements  in  them;  if  this  is  found  to  be  the 
case,  the  manubrial  cells  from  an  antheridium 
should  be  used  instead. 

b.  Tradescantia.     Examine  in  water,  with  a  high 
power,  the  hairs  which  grow  upon  the  stamens  : 
they  consist  of  a  row  of  large  roundish  cells, 
each  with  sac,  protoplasm,  nucleus,  and  vacuolar 
spaces.     Note  the  protoplasm;   partly  forming 
a  layer  (primordial  utricle)  lining  the  sac  and 
heaped  up  round  the  nucleus,  and  partly  form- 
ing bridles  running  across  the  cell  in  various 
directions  from  the  neighbourhood  of  the  nu- 
cleus, and  from  one  part  of  the  protoplasm  to 
another;  observe  the  currents  in  these  bridles; 
from  the  nucleus  in  some,  towards  it  in  others. 

c.  Vallisneria.    Take  a  leaf  beginning  to  look  old; 
split  it  into  two  layers  with  a  sharp  knife  and 
mount  a  bit  in  water;   examine  with  a  high 


54  ELEMENTARY  BIOLOGY.  [CHAP.  vi. 

power.  Note  the  larger  rectangular  cells,  be- 
longing to  the  deeper  layers,  with  well-marked 
currents  in  them,  which  carry  the  chlorophyll 
granules  round  and  round  inside  the  cell-wall. 

If  no  currents  are  seen  at  first,  gently  warm 
the  leaf  by  immersing  it  for  a  short  time  in 
water  heated  to  a  temperature  between  30°  and 
35°  C. 

d.  Anacharis.     Take    a    yellowish-looking    leaf: 
mount  in  water  and  examine  with  a  high  power; 
the  phenomena  observed  are  like  those  in  Val- 
lisneria.     They  are  best  observed  in  the  single 
layer  of  cells  at  the  margin  of  the  leaf. 

e.  Nettle-hair.    Mount  an  uninjured  hair  in  water 
with  the  bit  of  leaf  to  which  it  is  attached 
(it  is  essential  that  the  terminal  recurved  part 
of  the  large  cell  forming  the  hair  be  not  broken 
off);  examine  with  the  highest  available  power: 
currents  carrying  along  very  fine  granules  will 
be  seen  in  the  cell,  their  general  direction  being 
that  of  its  long  axis. 


VII. 
THE  BRACKEN   FERN   (Pteris  aquilina). 

THE  conspicuous  parts  of  this  plant  are  the  large  green 
leaves,  or  fronds,  which  rise  above  the  ground,  sometimes 
to  the  height  of  five  or  six  feet,  and  consist  of  a  stem-like 
axis  or  rachis,  from  which  transversely  disposed  offshoots 
proceed,  these  ultimately  subdividing  into  flattened  leaflets, 
the  pinnules.  The  rachis  of  each  frond  may  be  followed  for 
some  distance  into  the  ground.  Its  imbedded  portion  ac- 
quires a  brown  colour,  and  eventually  passes  into  an  irre- 
gularly branched  body,  also  of  a  dark-brown  colour,  which 
is  commonly  called  the  root  of  the  fern,  but  is,  in  reality,  a 
creeping  underground  stem,  or  rhizome.  From  the  surface 
of  this,  numerous  filamentous  true  roots  are  given  off. 
Traced  in  one  direction  from  the  attachment  of  the  frond, 
the  rhizome  exhibits  the  withered  bases  of  fronds,  developed 
in  former  years,  which  have  died  down ;  while,  in  the 
opposite  direction,  it  ends,  sooner  or  later,  by  a  rounded 
extremity  beset  with  numerous  fine  hairs,  which  is  the  apex, 
or  growing  extremity,  of  the  stem.  Between  the  free  end 
and  the  fully  formed  frond  one  or  more  processes,  the  rudi- 
ments of  fronds,  which  will  attain  their  full  development  in 
following  years,  are  usually  found. 

The  attachments   of  the  fronds  are  nodes,  the  spaces 
between  two  such  successive  attachments,  internodes.     It 


56  ELEMENTARY  BIOLOGY.  [CHAP. 

will  be  observed  that  the  internodes  do  not  become  crowded 
towards  the  free  end,  and  there  is  nothing  comparable  to 
the  terminal  bud  of  Chara  with  its  numerous  rudimentary 
appendages. 

When  the  fronds  have  attained  their  full  size,  the  edges 
of  the  pinnules  will  be  observed  to  be  turned  in  towards 
the  underside,  and  to  be  fringed  with  numerous  hair-like 
processes  which  roof  over  the  groove,  enclosed  by  the 
incurved  edge.  At  the  bottom  of  the  groove,  brown 
granular  bodies  are  aggregated,  so  as  to  form  a  streak 
along  each  side  of  the  pinnule.  The  granules  are  the 
sporangia,  and  the  streaks  formed  by  their  aggregation, 
the  son. 

Examined  with  a  magnifying  glass,  each  sporangium  is 
seen  to  be  pouch-shaped,  like  two  watch-glasses  united  by 
a  thick  rim.  When  ripe,  it  has  a  brown  colour,  readily 
bursts,  and  gives  exit  to  a  number  of  minute  bodies  which 
are  the  spores. 

The  plant  now  described  is  made  up  of  a  multitude  of 
cells,  having  the  same  morphological  value  as  those  of 
Chara,  and  each  consisting  of  a  protoplasmic  mass,  a 
nucleus  and  a  cellulose  wall.  These  cells,  however,  become 
very  much  modified  in  form  and  structure  in  different 
regions  of  the  body  of  the  plant,  and  give  rise  to  groups  of 
structures  called  tissues,  hi  each  of  which  the  cells  have 
undergone  special  modifications.  These  tissues  are,  to  a 
certain  extent,  recognizable  by  the  naked  eye.  Thus,  a 
transverse  section  of  the  rhizome  shews  a  circumferential 
zone  of  the  same  dark-brown  colour  as  the  external  epi- 
dermis t  enclosing  a  white  ground-substance,  interrupted  by 
variously  disposed  bands,  patches,  and  dots,  some  of  which 
are  of  the  same  dark-brown  hue  as  the  external  zone,  while 
others  are  of  a  pale  yellowish-brown. 


vir.]  THE  BRACKEN  FERN.  57 

The  dark-brown  dots  are  scattered  irregularly,  but  the 
major  part  of  the  dark-brown  colour  is  gathered  into  two 
narrow  bands,  which  lie  midway  between  the  centre  and 
the  circumference.  Sometimes  the  ends  of  these  bands  are 
united.  Enclosed  between  these  narrow,  dark-brown  bands 
are,  usually,  two  elongated,  oval,  yellowish-brown  bands ; 
and,  outside  them,  lie  a  number  of  similarly  coloured 
patches,  one  of  which  is  usually  considerably  longer  than 
the  others. 

A  longitudinal  section  shews  that  each  of  these  patches 
of  colour  answers  to  the  transverse  section  of  a  band  of 
similar  substance,  which  extends  throughout  the  whole 
length  of  the  stem ;  sometimes  remaining  distinct,  some- 
times giving  off  branches  which  run  into  adjacent  bands, 
and  sometimes  uniting  altogether  with  them. 

At  a  short  distance  below  the  apex  of  the  stem,  however, 
the  colour  of  all  the  bands  fades  away,  and  they  are 
traceable  into  mere  streaks,  which  finally  disappear  alto- 
gether in  the  semi-transparent  gelatinous  substance  which 
forms  the  growing  end  of  the  stem.  Submitted  to  micro- 
scopic examination,  the  white  ground-substance,  or  paren- 
chyma, is  seen  to  consist  of  large  polygonal  cells,  containing 
numerous  starch  granules;  and  the  circumferential  zone 
is  formed  of  somewhat  elongated  cells,  the  thick  walls  of 
which  have  acquired  a  dark-brown  colour,  and  contain 
little  or  no  starch.  The  dark-brown  bands,  on  the  other 
hand,  consist  of  cells  which  are  so  much  elongated  as 
almost  to  deserve  the  name  of  fibres  and  constitute  what 
is  termed  sderenchyma.  Their  walls  are  very  thick,  and  of 
a  deep-brown  colour;  but  the  thickening  has  taken  place 
unequally,  so  as  to  leave  short,  obliquely  directed,  thin 
places,  which  look  like  clefts.  The  yellow  bands,  lastly, 
are  vascular  bundles.  Each  consists,  externally,  of  thick- 


58  ELEMENTARY  BIOLOGY.  [CHAP. 

walled,  elongated,  parallel-sided  cells,  internal  to  which  lie 
elongated  tubes  devoid  of  protoplasm,  and  frequently  con- 
taining air.  In  the  majority  of  these  tubes,  and  in  all 
the  widest,  the  walls  are  greatly  thickened,  the  thickening 
having  taken  place  along  equidistant  transverse  lines.  The 
tubes  have  become  flattened  against  one  another,  by  mutual 
pressure,  so  that  they  are  five-  or  six-sided ;  and,  as  the 
markings  of  their  flattened  walls  simulate  the  rounds  of  a 
ladder,  they  have  been  termed  scalariform  ducts  or  vessels. 
The  cavities  of  these  scalariform  ducts  are  divided  at 
intervals,  in  correspondence  with  the  lengths  of  the  cells 
of  which  they  are  made  up,  by  oblique,  often  perforated, 
partitions.  Among  the  smaller  vessels,  a  few  will  be  found, 
in  which  the  thickening  forms  a  closely  wound  spiral. 
These  are  spiral  vessels. 

The  rachis  of  a  frond,  so  far  as  it  projects  above  the 
surface  of  the  ground,  is  of  a  bright  green  colour ;  and,  in 
transverse  section,  it  presents  a  green  ground-substance, 
interrupted  by  irregular  paler  markings,  which  are  the  trans- 
verse sections  of  longitudinal  bands  of  a  similar  colour. 
There  are  no  brown  spots  or  bands.  Examined  micro- 
scopically, the  ground-substance  is  found  to  be  composed 
of  polygonal  cells  containing  chlorophyll.  These  are 
invested  superficially  by  an  epidermis,  composed  of  elon- 
gated cells,  with  walls  thickened  in  such  a  manner  as  to 
leave  thin  circular  spots  here  and  there.  Hence,  those 
walls  of  the  cells,  which  are  at  right  angles  to  the  axis  of 
vision,  appear  dotted  with  clear  spots;  while,  in  those 
walls  of  which  transverse  sections  are  visible,  the  dots  are 
seen  to  be  funnel-shaped  depressions. 

The  pale  bands  are  vascular  bundles  containing  scalari- 
form and  spiral  vessels.  The  outer  layer  investing  each 
is  chiefly  formed  of  long  hollow  fibres  with  very  thick 


vi  T.]  THE  BRACKEN  FERN.  59 

walls,  and  terminating  in  a  point  at  each  end.  These 
sclerenchymatousy^m1  have  oblique  cleft-like  clear  spaces, 
produced  by  interruptions  of  the  process  of  thickening  in 
their  walls. 

The  vascular  bundles,  the  green  parenchyma,  and  the 
epidermis  are  continued  into  each  pinnule  of  the  frond. 
The  epidermis  retains  its  ordinary  character  on  the  upper 
side  of  the  pinnule,  except  that  the  contours  of  its  com- 
ponent cells  become  somewhat  more  irregular.  On  the 
under  side,  many  hairs  are  developed  from  it,  and  the 
cells  become  singularly  modified  in  form,  their  walls  being 
thrown  out  into  lobes,  which  interlock  with  those  of  adja- 
cent cells. 

Between  many  of  these  cells  an  oval  space  is  left,  forming 
a  channel  of  communication  between  the  interior  of  the 
frond  and  the  exterior.  The  opening  of  this  space  is  sur- 
mounted by  two  reniform  cells,  the  concavities  of  which 
are  turned  towards  one  another,  while  their  ends  are  in 
contact.  The  opening  left  between  the  applied  concave 
faces  is  a  stomate;  and,  as  the  stomata  are  present  in 
immense  numbers,  there  is  a  free  communication  between 
the  outer  air  and  the  intercellular  passages  which  exist 
in  the  substance  of  the  frond.  Those  cells  of  the  green 
parenchyma  of  the  frond  which  form  the  inferior  half  of  its 
thickness,  in  fact,  are  irregularly  elongated,  and  frequently 
produced  into  several  processes,  or  stellate.  They  come  into 
contact  with  adjacent  cells  only  by  comparatively  small 
parts  of  their  surfaces,  or  by  the  ends  of  these  processes. 
They  thus  bound  passages  between  the  cells,  intercellular 
passages,  which  are  full  of  air,  and  are  in  communication 
with  similar,  but  narrower,  passages,  which  extend  through- 
out the  substance  of  the  plant. 

The  vascular  bundles   break  up  in  the  pinnules,  and 


60  ELEMENTARY  BIOLOGY.  [CHAP. 

follow  the  course  of  the  so-called  veins  which  are  visible 
upon  its  surface;  ducts  being  continued  into  their  ultimate 
ramifications. 

The  rootlets  present  an  outer  coat  of  epidermis,  enclosing 
parenchyma  traversed  by  a  central  vascular  bundle.  They 
increase  in  length  by  the  division  and  subdivision  of  the 
cells  at  the  growing  point,  but  this  point  is  not  situated  at 
the  very  surface  of  the  rootlet,  as  the  growing  point  at  the 
extremity  of  the  rhizome  is,  but  is  covered  by  a  cap  of  cells. 

When  the  spores  are  sown  upon  damp  earth,  or  a  tile, 
or  a  slip  of  glass,  and  kept  thoroughly  moist  and  warm, 
they  germinate.  Each  gives  rise  to  a  tubular,  hypha-like 
prolongation,  which  developes  a  similar  process,  the  primi- 
tive rootlet,  close  to  the  spore.  The  hypha-like  prolongation, 
at  first,  undergoes  transverse  division,  so  that  it  becomes 
converted  into  a  series  of  cells.  Then,  the  cells  at  its  free 
end  divide  longitudinally,  as  well  as  transversely,  and  thus 
give  rise  to  a  flat  expansion,  which  gradually  assumes  a 
bilobed  form,  and  becomes  thickened,  in  some  parts,  by 
division  of  its  cells  in  a  direction  perpendicular  to  its 
surface.  The  protoplasm  of  these  cells  developes  chlorophyll 
granules,  whereby  the  bilobed  disk  acquires  a  green  colour ; 
while  numerous  simple  radicle  fibres  are  given  off  from 
its  under  surface,  and  attach  the  little  plant,  which  is 
termed  a  prothallus  we  prothallium,  to  the  surface  on  which 
it  grows. 

The  prothallus  attains  no  higher  development  than  this, 
and  does  not  directly  grow  into  a  fern  such  as  that  in  which 
the  spores  took  their  origin ;  but,  after  a  time,  rounded  or 
ovoidal  elevations  are  developed,  by  the  outgrowth  and 
division  of  the  cells  which  form  its  under  aspect.  Some  of 
these  are  antheridia.  The  protoplasm  of  each  of  the  cells 
contained  in  their  interior  is  converted  into  an  antherozooid, 


VII.]  THE  BRACKEN  FERN.  61 

somewhat  similar  to  that  of  Chara,  but  provided  with  many 
more  cilia.  The  antheridium  bursts,  and  the  antherozooids, 
set  free  from  their  containing  cells,  are  propelled  through 
the  moisture  on  the  under  surface  of  the  prothallus  by  their 
cilia. 

The  processes  of  the  second  kind  acquire  a  more  cylin- 
drical form,  and  are  called  archegonia.  Of  the  cells  which 
are  situated  in  the  axis  of  the  cylinder,  all  disappear  but 
that  which  lies  at  the  bottom  of  its  cavity.  This  is  the 
embryo  cell,  and  when  the  archegonium  is  fully  formed,  a 
canal  leads  from  its  summit  to  this  cell.  The  antherozooids 
enter  by  this  canal,  and  impregnate  the  embryo  cell. 

The  embryo  cell  now  begins  to  divide,  and  becomes 
converted  into  four  cells ;  of  these,  the  two  which  lie  at  the 
deepest  part  of  the  cavity  of  the  archegonium  subdivide  and 
ultimately  form  a  plug-like,  cellular,  mass,  which  imbeds 
itself  firmly  in  the  substance  of  the  prothallus.  Of  the  re- 
maining two  cells,  which  also  undergo  subdivision,  one  gives 
rise  to  the  rhizome  of  the  young  fern,  while  the  other  becomes 
its  first  rootlet.  It  appears  probable  that  the  plug-like  mass 
absorbs  nutritive  matter  from  the  prothallus,  and  supplies 
the  rhizome  of  the  young  fern,  until  it  is  able  to  provide  for 
itself.  As  the  rhizome  grows,  and  developes  its  fronds,  it 
rapidly  attains  a  size  vastly  superior  to  that  of  the  prothallus, 
which  at  length  ceases  to  have  any  functional  importance, 
and  disappears. 

Thus  Pteris  presents  a  remarkable  case  of  the  alternation 
of  generations.  The  large  and  complicated  organism  com- 
monly known  as  the  'Fern'  is  the  product  of  the  impreg- 
nation of  the  embryo  cell  by  the  antherozooid.  This  'Fern,' 
when  it  attains  its  adult  condition,  developes  sporangia ;  and 
the  inner  cells  of  these  sporangia  give  rise,  by  a  perfectly 
asexual  fissive  process,  to  the  spores.  The  spores  when  set 


62  ELEMENTARY  BIOLOGY.  [CHAP. 

free  germinate;  the  product  of  that  germination  is  the  incon- 
spicuous and  simply  cellular  prothallus;  an  independent 
organism,  which  nourishes  itself  and  grows,  and  on  which, 
eventually,  the  essential  organs  of  the  sexual  process — the 
archegonia  and  antheridia — are  developed. 

Each  impregnated  embryo  cell  produces  only  a  single 
'fern,'  but  each  'fern'  may  give  rise  to  innumerable  pro- 
thallia,  seeing  that  every  one  of  the  numerous  spores  de- 
veloped in  the  immense  multitude  of  sporangia  to  which  the 
frond  gives  rise,  may  germinate. 


LABORATORY  WORK. 

A.    THE  FERN-PLANT;  ASEXUAL  GENERATION. 
a.    External  characters. 

a.  The  brown  underground  stem  or  rhizome,  with 
a  lighter  band  (the  lateral  line)  running  along 
each  side  of  it :  its  nodes  and  internodes. 

b.  The  roots  springing  from  the  rhizome. 

c.  The  leaves  or  fronds  arising  from  the  rhizome  at 
intervals,  along  the  lateral  lines. 

a.  The  great  amount  of  subdivision  of  the  frond : 
its  main  axis  (rachis)  ;  the  primary  divisions  or 
pinna;  the  ultimate  divisions  or  pinnules. 

/?.  The  sort;  small  brown  patches  along  the 
margin  of  the  under  surface  of  some  of  the 
pinnules. 

d.  The  nodes  and  internodes  of  the  rhizome.     The 
absence  of  a  terminal  bud  on  it. 


THE  "|L 

RSrfY   I 


vii.]  THE  BRACKEN  FERN.  63 

T).    The  rhizome. 

1.  Cut  it  across  and  draw  the  section  as  seen  with  the 
naked  eye. 

a.  The  outer  brownish  layer  (epidermis  and  sub- 
epidermis)  ;    the   latter  thins   away   somewhat, 
opposite  the  lateral  lines. 

b.  The  yellowish-white  substance  (ground-substance 
or  parenchyma)  forming  most  of  the  thickness  of 
the  section. 

c.  The  internal  incomplete  brown  ring  (sclerenchyma) 
imbedded  in  the  parenchyma. 

d.  The   small  patches  of  sclerenchyma  scattered 
about   in  the    parenchyma  outside  the  main 
sclerenchymatous  ring. 

e.  The  yellowish  tissue  (vascular,  bundles)  lying  in- 
side and  outside  the  ring  of  sclerenchyma. 

2.  Cut  a  longitudinal  section  of  the  rhizome ;  make  out 
on  the  cut  surface  b.  i.  a,  b,  c,  d. 

3.  Cut  a  thin  transverse  section  of  the  rhizome,  mount 
in  water  and  examine  with  i  inch  obj. 

a.  The  single  layer  of  much  thickened  epidermic 
cells. 

b.  The  small  opaque  angular  contours  of  the  sub- 
epidermic  cells  (external  sclerenchyma}. 

c.  The  large  polyhedral  more  transparent  paren- 
chymatous  cells. 

d.  The  small  opaque  angular  contours  of  the  cells 
of  the  internal  sclerenchyma. 

e.  The  great  openings  of  the  ducts  and  vessels  in 
the  nbro-vascular  bundles. 

Draw  the  section. 


<54  ELEMENTARY  BIOLOGY.  [CHAP. 

4.      Examine  with  \  obj. 

a.  The  epidermis ;  its  thick-walled  cells; 

b.  The  parenchyma ;  its  large  thin- walled  cells :  their 
sac,  protoplasm  and  nucleus  :  the  great  number 
of  starch  granules  in  them. 

c.  The  various  patches  of  sclerenchyma,  made  up  of 
thick-walled  angular  cells. 

d.  The  vasctilar  bundles.     Note  in  each  : — 

a.  Outside,  a  single  layer  of  cells  containing  no 
starch  granules  (bundle  sheath).  These  really 
belong  to  the  parenchyma  or  ground  tissue. 

/?.  Within  the  bundle  sheath  a  layer  of  small 
parenchymatous  cells  containing  starch  (inner 
or  bast  sheath). 

y.  Within  the  last  layer  comes  the  bast  of  the 
bundle  (phloem)  consisting  of— externally,  two 
or  more  layers  of  small  rectangular  cells  with 
thickened  walls  (bast  fibres)  and  then  a  single 
row  of  large  thin-walled  cells  (bast  vessels) 
between  which  lie  smaller  thin-walled  cells 
containing  starch  granules  (bast  parenchyma). 

8.  Within  the  bast  are  seen  the  cross  sections 
of  the  vessels:  note  their  greatly  thickened 
walls,  and  large  central  cavity  containing  no 
protoplasm. 

c.       Scattered  here  and  there,  in  the  spaces  between 
the  angles  of  the  vessels,  are  small  parenchy- 
matous cells   (wood  parenchyma)  containing 
starch  granules. 
The  wood,  or  xylem,  consists  of  8  and  e. 

£.  Treat  with  iodine:  the  protoplasm  stained 
brown;  the  starch  granules  deep  blue',  render- 


VIL]  THE  BRACKEN  FERN.  65 

ing  some  of  the  cells  quite  opaque  and  almost 
black-looking. 

5.  Cut  a  thin  longitudinal  section  of  the  stem  and 
examine  with  i  inch  and  then  with  ~  obj.  Make 
out  the  various  tissues  described  in  3  and  4. 

a.  The  epidermis,   subepidermis  and  parenchyma, 
much  as  in  the  transverse  section,  except  that 
the  subepidermic  cells  are  longer. 

b.  The  sclerenchyma  is  seen  to  be  made  up  of  greatly 
elongated  cells,  tapering  towards  each  end. 

c.  The  vascular  bundles;  note  in  them — 

a.  The  cells  of  the  bundle  sheath  much  as  in  the 
transverse  section;  the  bast  fibres,  elongated, 
with  thickened  walls;  the  cells  of  the  bast 
parenchyma  somewhat  elongated  ;  the  bast 
vessels,  elongated  cells,  presenting  irregular 
patches  of  pores  (sieve-tubes) ;  the  bast  sheath 
cells  somewhat  elongated. 

ft.  The  vessels:  elongated  tubes  presenting  cross 
partitions,  dividing  them  into  separate  cells, 
at  long  intervals.  Two  forms  of  vessel  will 
be  seen,  viz.  scalariform  vessels,  with  regular 
transverse  thickenings  on  their  walls  and 
spiral  vessels,  less  numerous  than  the  last 
form :  with  a  continuous  spiral  thickening  on 
their  walls. 

•y.  The  bast  cells:  seven  or  eight  times  as  long  as 
they  are  broad,  and  terminating  obliquely  at 
each  end. 

8.      The  elongated  larger  cells  (4.  d.  8) :  they  have 
very  slightly  thickened  walls  and  no  scalari- 
form markings. 
M.  5       • 


66  ELEMENTARY  BIOLOGY.  [CHAP. 

6.  [Cut  off  half  an  inch  of  the  growing  end  of  the  steir, 
imbed  it  in  paraffin  upside  down,  and  cut  a  series  of 
transverse  sections :  examine  them  with  the  microscope, 
beginning  with  those  farthest  from  the  growing  point. 
At  first  the  various  tissues  described  in  3  and  4  will  be 
readily  recognisable;  as  the  sections  nearer  the  grow- 
ing point  are  examined  they  will  be  less  distinct,  and 
close  to  the  growing  point  the  whole  section  will  be 
found  to  be  composed  entirely  of  parenchymatous 
closely-fitting  cells.] 

[c.    The  leaf.     Imbed  a  leaf  in  paraffin  and  cut  a  thin 

vertical  section :  examine  with  i  inch  obj.  It  will  be 

found  to  be  constructed  essentially  on  the  same  plan 
as  the  leaf  of  the  bean.    (VI 1 1.)] 

d.    The  reproductive  organs. 

T.  Examine  a  sorus  with  a  low  power  without  a  cover- 
glass.  It  is  composed  of  a  great  number  of  minute 
oval  bodies,  the  sporangia. 

2.  Scrape  off  some  sporangia  and  mount  in  water:    ex- 
amine with  i  inch  obj. 

a.  Their  form ;    they  are   oval  biconvex   bodies 
borne  on  a  short  stalk. 

b.  Their  structure:  composed  of  brownish  cells,  one 
row  of  which  has  very  thick  walls,  and  forms  a 
marked  ring  (annufos)  round  the  edge  of  the 
sporange. 

c.  Their  mode  of  dehiscencf  (look  out  for  one  that 
has   opened):   by  a  cleft  running  towards  the 
centre  of  the  sporange.  from  a  point  where  the 
annulus  has  torn  across. 

3.  Burst  open  some  sporangia  by  pressing  on  the  cover- 
glass:  examine,  with  \  obj.,. the  spores  which  are  set 
free. 


vii.]  THE  BRACKEN  FERN,  67 

a.  Their  size:  measure. 

b.  TJieirform:  somewhat  triangular. 

[c.  Their  structure:  a  thick  outer  coat,  a  thin  inner 
coat,  protoplasm,  and  a  nucleus:  crush  some  by 
pressure  on  the  cover-glass.] 

B.     THE  PROTHALLUS;  SEXUAL  GENERATION, 

Prothalli  may  be  obtained  by  sowing  some  spores  on  a 
glass  slide,  and  keeping  them  warm  and  very  moist  for  about 
three  months.  They  are  small  deep  green  leaf-like  bodies. 

a.    The  Prothallus. 

i  .  Transfer  a  prothallus  to  a  slide,  and  mount  it  in  water 
with  its  under  surface  uppermost.  Examine  with  i 
inch  obj. 

a.  Its  form:  a  thin  kidney-shaped  expansion  from 
which,  especially  towards  its  convex  border,  a 
number  of  slender  filaments  (rootlets)  arise. 

b.  Its  structure. 

a.  The  leafy  expansion :  it  consists  throughout 
most  of  its  extent  of  a  single  layer  of  polyhe- 
dral chlorophyll-containing  cells,  but  at  a  part 
(the  cushion]  a  little  behind  the  depression 
marking  the  growing  point  it  is  several  cells 
thick. 

/?.  The  rootlets:  composed  of  a  series  of  cells 
which  contain  no  chlorophyll. 

c.  The  antheridia  and  archegonia:  the  former  can 
just  be  seen  with  an  inch  objective  as  minute 
eminences  on  the  under  surface  of  those  parts  of 
the  prothallus  which  consist  of  a  single  layer 

-   of  cells,  especially  among  the  root-hairs ;   the 
latter  are  partly  imbedded  in  the  cushion. 

5—2 


68  ELEMENTARY  BIOLOGY.  [CHAP. 

b.    The  reproductive  organs. 

These  are  to  be  found  by  examining  the  under  surface  of 
the  prothallus  with  J  obj. 

1.  The  antJieridia.    Most  numerous  near  and  among  the 
rootlets. 

a.  Their  form:  small  hemispherical  eminences. 

b.  Their  structure:  made  up  of  an  outer  layer  of 
cells  containing  a  few  chlorophyll-granules,  and 
through  which  can  be  seen,  according  to  the 
stage  of  development,  either  a  single  central  cell, 
or  a  number  of  smaller  cells  (mother-cells  of 
antherozooids}  resulting  from  its  division :  in  the 
latter  cells,  in  ripe  antheridia,  spirally  coiled 
bodies  (antherozooids]  can  be  indistinctly  seen. 

2.  The  antherozooids. 

Some  of  these  are  sure  to  be  found  swimming  about 
in  the  water  if  a  number  of  ripe  prothalli  are  examined. 

a.  Small  bodies,  coiled  like  a  corkscrew,  thick  at 
one  end,  and  tapering  towards  the  other,  which 
has  a  number  of  cilia  attached  to  it.     To  the 
thicker  end  of  the  antherozooid  is  often  attached 
a  rounded  mass  containing  colourless  granules. 

b.  Treat  with  iodine;  this  stains  them  and  stops 
their  movements,  so  that  their  form  can  be  more 
distinctly  seen. 

3.  The  archegonia.     Make  vertical  sections  of  the  pro- 
thallus passing  through  the  cushion;  either  by  simply 
chopping  down  it  with  a  razor,  or  holding  it  between 
two  pieces   of  carrot  and   cutting.      Note  in  the 
archegonia — 

a.      Their  form:  chimney-shaped  eminences  with  a 
small  aperture  at  the  apex. 


vii.]  THE  BRACKEN  FERN.  69 

b.  Their  structure.  Each  is  composed  of  a  layer 
of  transparent  cells  containing  no  chlorophyll, 
arranged  in  four  rows,  and  surrounding  a  central 
cavity  which  extends  into  the  cushion  formed  by 
the  thickened  part  of  the  prothallus  (a.  i.  b.  a). 
In  this  cavity  lies,  in  young  specimens,  a  large 
nucleated  granular  basal  cell,  with  two  or  three 
smaller  granular  cells  (neck-cells)  above  it  in  the 
narrow  upper  part  of  the  cavity;  in  older  speci- 
mens this  upper  part  is  empty,  forming  a  canal 
leading  down  to  the  basal  cell. 

4.     Examine    young  Fern    in  connection  with  its  pro- 
thallus. 


VIII. 
THE  BEAN-PLANT  (Vicia  faba). 

IN  this,  which  is  selected  as  a  convenient  example  of  a 
Flowering  Plant,  the  same  parts  are  to  be  distinguished  as 
in  the  Fern ;  but  the  axis  is  erect  and  consists  of  a  root  im- 
bedded in  the  earth  and  a  stem  which  rises  into  the  air.  The 
appendages  of  the  stem  are  leaves,  developed  from  the  op- 
posite sides  of  successive  nodes ;  and  the  internodes  become 
shorter  and  shorter  towards  the  summit  of  the  stem,  which 
ends  in  a  terminal  bud.  Buds  are  also  developed  in  the 
axils  of  the  leaves,  and  some  of  them  grow  into  branches, 
which  repeat  the  characters  of  the  stem ;  but  others,  when 
the  plant  attains  its  full  development,  grow  into  stalks  which 
support  the  flowers;  each  of  which  consists  of  a  calyx,  a 
corolla,  a  staminal  tube  and  a  central  pistil;  the  latter  is  ter- 
minated by  a  style,  the  free  end  of  which  is  the  stigma. 

The  staminal  tube  ends  in  ten  filaments,  four  of  which 
are  rather  shorter  than  the  rest;  and  the  filaments  bear  oval 
bodies,  the  anthers,  which,  when  ripe,  give  exit  to  a  fine 
powder,  made  up  of  minute  pollen  grains.  The  pistil  is 
hollow;  and,  attached  by  short  stalks  along  the  ventral  side 
of  it,  or  that  turned  towards  the  axis,  is  a  longitudinal  series 
of  minute  bodies,  the  ovufes.  Each  ovule  consists  of  a  central 
conical  nucleus,  invested  by  two  coats,  an  outer  and  an  inner. 
Opposite  the  summit  of  the  nucleus,  these  coats  are  per- 
forated by  a  canal,  the  micrcpyle,  which  leads  down  to  the 


vin.]  THE  BEAN-PLANT.  71 

nucleus.  The  nucleus  contains  a  sac,  the  embryo  sac,  in 
which  certain  cells,  one  of  which  is  the  embryo  cell,  and 
the  rest  endosperm  cells,  are  developed.  A  pollen  grain 
deposited  on  the  stigma,  sends  out  a  hypha-like  prolonga- 
tion, the  pollen  tube,  which  elongates,  passes  down  the  style, 
and  eventually  reaches  the  micropyle  of  an  ovule.  Travers- 
ing the  micropyle,  the  end  of  the  pollen  tube  penetrates  the 
nucleus,  and  comes  into  close  contact  with  the  embryo  sac. 
This  is  the  process  of  impregnation,  and  the  result  of  it 
is  that  the  embryo  cell  divides  and  give  rise  to  a  cellular 
embryo.  This  becomes  a  minute  Bean-plant,  consisting  of  a 
radicle  or  primary  root;  of  two,  relatively  large,  primary 
leaves,  the  cotyledons;  and  of  a  short  stem,  the  plumule,  on 
which  rudimentary  leaves  soon  appear.  The  cotyledons  now 
increase  in  size,  out  of  all  proportion  to  the  rest  of  the  em- 
bryonic plant;  and  the  cells  of  which  they  are  composed 
become  filled  with  starch  and  other  nutritious  matter.  The 
nucleus  and  coats  of  the  ovule  grow  to  accommodate  the 
enlarging  embryo,  but,  at  the  same  time,  become  merged 
into  an  envelope  which  constitutes  the  coat  of  the  seed.  The 
pistil  enlarges  and  becomes  the  pod;  this,  when  it  has 
attained  its  full  size,  dries  and  readily  bursts  along  its  edges, 
or  decays,  setting  the  seeds  free.  Each  seed,  when  placed 
in  proper  conditions  of  warmth  and  moisture,  then  germinates. 
The  cotyledons  of  the  contained  embryo  swell,  burst  the 
seed  coat,  and,  becoming  green,  emerge  as  the  fleshy  seed 
leaves.  The  nutritious  matters  which  they  contain  are  ab- 
sorbed by  the  plumule  and  radicle,  the  latter  of  which  de- 
scends into  the  earth  and  becomes  the  root,  while  the  former 
ascends  and  becomes  the  stem  of  the  young  bean-plant. 
The  apex  of  the  stem  retains,  throughout  life,  the  simply 
cellular  structure  which  is,  at  first,  characteristic  of  the  whole 
embryo ;  and  the  growth  in  length  of  the  stem,  so  far  as  it 


72  ELEMENTARY  BIOLOCY.  [CHAP. 

depends  on  the  addition  of  new  cells,  takes  place  chiefly,  if 
not  exclusively,  in  this  part. 

The  apex  of  the  root,  on  the  other  hand,  gives  rise  to  a 
root-sheath,  as  in  the  Fern. 

The  leaves  cease  to  grow  by  cell  multiplication  at  their 
apices,  when  these  are  once  formed,  the  addition  of  new 
cells  taking  place  at  their  bases. 

The  tissues  which  compose  the  body  of  the  Bean-plant 
are  similar,  in  their  general  characters,  to  those  found  in  the  • 
Fern,  but  they  differ  in  the  manner  of  their  arrangement. 
The  surface  is  bounded  by  a  layer  of  epidermic  cells,  within 
which,  rounded  or  polygonal  cells  make  up  the  ground- 
substance,  or  parenchyma,  of  the  plant,  extending  to  its 
very  centre  in  the  younger  parts  of  the  stem  and  in  the  root; 
while,  in  the  older  parts  of  the  stem,  the  centre  is  occupied 
by  a  more  or  less  considerable  cavity,  full  of  air.  This 
cavity  results  from  the  central  parenchyma  becoming  torn 
asunder,  after  it  has  ceased  to  grow,  by  the  enlargement  of 
the  peripheral  parts  of  the  stem.  Nearer  to  the  circumfer- 
ence than  to  the  centre,  lies  a  ring  of  woody  and  vascular 
tissue,  which,  in  transverse  sections,  is  seen  to  be  broken  up 
into  wedge-shaped  bundles,  by  narrow  bands  of  parenchy- 
matous  tissue,  which  extend  from  the  parenchyma  within 
the  circle  of  woody  and  vascular  tissue  (medulla  or  pith)  to 
that  which  lies  outside  it.  Moreover,  each  bundle  of  woody 
and  vascular  tissue  is  divided  into  two  parts,  an  outer  and 
an  inner,  by  a  thin  layer  of  small  and  very  thin-walled  cells, 
termed  the  cambium  layer.  What  lies  outside  this  layer 
belongs  to  the  bark  and  epidermis;  what  lies  inside  it,  to 
the  wood  and  pith. 

The  great  morphological  distinction  between  the  axis  of 
the  Bean  and  that  of  the  Fern  lies  in  the  presence  of  this 
cambium  layer.  The  cells  composing  it,  in  fact,  retain 


viii.]  THE  BEAN-PLANT.  73 

their  power  of  multiplication,  and  divide  by  septa  parallel 
with  the  length  of  the  stem,  or  root,  as  well  as  transverse  to 
it.  Thus  new  cells  are  continually  being  added,  on  the 
inner  side  of  the  cambium  layer,  to  the  thickness  of  the 
wood,  and  on  the  outer  side  of  it,  to  the  thickness  of  the 
bark;  and  the  axis  of  the  plant  continually  increases  in 
diameter,  so  long  as  this  process  goes  on.  Plants  in  which 
this  constant  addition  to  the  outer  face  of  the  wood  and  the 
inner  face  of  the  bark  takes  place,  are  termed  exogens. 

At  the  apex  of  the  stem,  and  at  that  of  the  root,  the 
cambium  layer  is  continuous  with  the  cells,  which  retain 
the  capacity  of  dividing  in  these  localities.  As  the  plant  is 
thickest  at  the  junction  of  the  stem  and  root,  and  diminishes 
thence  to  the  free  ends,  or  apices,  of  these  two  structures, 
the  cambium  layer  may  be  said  to  have  the  form  of  a  double 
cone.  And  it  is  the  special  peculiarity  of  an  exogen  to 
possess  this  doubly  conical  layer  of  constantly  dividing 
cells,  the  upper  end  of  which  is  free,  at  the  growing  point 
of  the  terminal  bud  of  the  stem,  while  its  lower  end  is 
covered  by  the  root-cap  of  the  ultimate  termination  of  the 
principal  root. 

The  most  characteristic  tissues  of  the  wood  are  dotted 
ducts  and  spiral  vessels,  the  spiral  vessels  being  particularly 
abundant  close  to  the  pith.  The  bark  contains  elongated 
liber  or  bast  cells;  but  there  are  no  scalariform  vessels  such 
as  are  found  in  the  Fern. 

Stomates  are  absent  in  the  epidermis  of  the  root:  they 
are  to  be  found,  here  and  there,  in  the  epidermis  of  all  the 
green  parts  of  the  stem  and  its  appendages,  but,  as  in  the 
Fern,  they  are  most  abundant  in  the  epidermis  of  the  under 
side  of  the  leaves.  As  in  the  Fern,  they  communicate  with 
intercellular  passages,  which  are  widest  in  the  leaves,  but 
extend  thence  throughout  the  whole  plant. 


74  ELEMENTARY  BIOLOGY.  [CHAP. 

The  difference  between  a  flowering  plant,  such  as  the 
Bean,  and  a  flowerless  plant,  such  as  the  Fern,  at  first  sight 
appears  very  striking,  but  it  has  been  proved  that  the  two 
are  but  the  extreme  terms  of  one  series  of  modifications. 
The  anther,  for  example,  is  strictly  comparable  to  a  sporan- 
gium.    The  pollen  grains  answer  to  the  male  spores  of  those 
flowerless  plants  in  which  the  spores  are  of  distinct  sexes — 
some  spores  giving  rise  to  prothallia  which  develope  only 
antheridia,  and  others  to  prothallia  which  develope  only 
archegonia;   instead  of  the  same  prothallia  producing  the 
organs  of  both  sexes,  as  in  Pteris.     And  the  pollen  tube  cor- 
responds with  the  first  hypha-like  process  of  the  spore.     But, 
in  the  flowering  plants,  the  protoplasm  of  the  pollen  tube 
does  not  undergo  division  and  conversion  into  a  prothallus, 
from  which  antheridia  are  developed,  giving  rise   to   de- 
tached fertilizing  bodies   or  antherozooids,   but   exerts  its 
fertilizing  influence  without  any  such  previous  differentia- 
tion.    The   connecting  links   between  these  two   extreme 
modifications  are  furnished,  on  the  one  hand,  by  the  Coni- 
fers, in  which  the  protoplasm  of  the  pollen  tube  becomes 
divided  into  cells,  from  which,  however,  no  antherozooids 
are  developed;   and  the  Club-mosses,  in  which  the  proto- 
plasm of  the  male  spores  (=  pollen  grains)  divides  into  cells 
which  form  no  prothallus,  but  give  rise  directly  to  anthero- 
zooids. 

On  the  other  hand,  the  embryo  sac  is  the  equivalent  of  a 
female  spore:  the  endosperm  cells,  which  are  produced  from 
part  of  its  protoplasm,  answer  to  the  cells  of  a  prothallus; 
while  the  embryo  cell  of  the  flowering  plant  corresponds 
with  the  embryo  cell  contained  in  the  archegonium  of  the 
prothallus.  In  the  development  of  the  female  spore  of  the 
flowering  plant,  therefore,  the  free  prothallus  and  the  arche- 

gonia  are  suppressed.     Here,  again,  the  intermediate  stages 


vin.]  THE  BEAN-PLANT.  75 

are  presented  by  the  Conifers  and  the  Club-mosses.  For, 
in  the  Conifers,  the  protoplasm  of  the  embryo  sac  gives 
rise  to  a  solid  prothallus-like  endosperm,  in  which  bodies 
called  corpusciila,  which  answer  to  the  archegonia,  are  formed; 
and  in  these  the  embryo  cells  arise;  while,  in  some  of  the 
Club-mosses,  there  are  female  spores  distinct  from  the  male 
spores,  and  the  prothallus  which  they  develope  does  not 
leave  the  cavity  of  the  spore,  but  remains  in  it  like  an 
endosperm. 

The  physiological  processes  which  go  on  in  the  higher 
green  plants,  such  as  the  Fern  and  the  Bean,  resemble, 
in  the  gross,  those  which  take  place  in  Prvt&coccus  and 
Cham.  For  such  plants  grow  and  flourish  if  their  roots 
are  immersed  in  water  containing  a  due  proportion  of 
certain  saline  matters,  while  their  stem  and  leaves  are  ex- 
posed to  the  air,  and  receive  the  influence  of  the  sun's  rays. 

A  Bean-plant,  for  instance,  may  be  grown,  if  supplied 
through  its  roots  with  a  dilute  watery  solution  of  potassium 
and  calcium  nitrate,  potassium  and  iron  sulphate,  and  mag- 
nesium sulphate.  While  growing  it  absorbs  the  solution, 
the  greater  part  of  the  water  of  which  evaporates  from  the 
extensive  surface  of  the  plant.  In  sunshine,  it  rapidly 
decomposes  carbonic  anhydride,  fixing  the  carbon,  and 
setting  free  the  oxygen ;  at  night,  it  slowly  absorbs  oxygen, 
and  gives  off  carbonic  acid ;  and  it  manufactures  a  large 
quantity  of  protein  compounds,  cellulose,  starch,  sugar  and 
the  like,  from  the  raw  materials  supplied  to  it. 

It  is  further  clear  that,  as  the  decomposition  of  carbonic 
anhydride  can  take  place  only  under  the  combined  in- 
fluences of  chlorophyll  and  sunlight,  that  operation  must 
be  confined,  in  all  ordinary  plants,  to  the  tissue  imme- 
diately beneath  the  epidermis  in  the  stem,  and  to  the 


76  ELEMENTARY  BIOLOGY.  [CHAP. 

leaves.  And  it  can  be  proved,  experimentally,  that  fresh 
green  leaves  possess  this  power  to  a  remarkable  extent. 

On  the  other  hand,  it  is  clear  that,  when  a  plant  is  grown 
under  the  conditions  described,  the  nitrogenous  and  mineral 
constituents  of  its  food  can  reach  the  leaves  only  by  passing 
from  the  roots,  where  they  are  absorbed,  through  the  stem 
to  the  leaves.  And,  at  whatever  parts  of  the  plant  the  nitro- 
genous and  mineral  constituents  derived  from  the  roots 
are  combined  with  the  carbon  fixed  in  the  leaves,  the 
resulting  compound  must  be  diffused  thence,  in  order  to 
reach  the  deep-seated  cells,  such  for  instance  as  those  of 
the  cambium  layer  and  those  of  the  roots,  which  are 
growing  and  multiplying,  and  yet  have  no  power  of  ex- 
tracting carbon  directly  from  carbonic  anhydride.  In  fact, 
those  cells  which  contain  no  chlorophyll,  and  are  out  of 
the  reach  of  light,  must  live  after  the  fashion  of  Torula; 
and  manufacture  their  protein  out  of  a  material  which 
contains  nitrogen  and  hydrogen,  with  oxygen  and  carbon, 
in  some  other  shape  than  that  of  carbonic  anhydride.  The 
analogy  of  Torula  suggests  a  fluid  which  contains  in  solu- 
tion, either  some  ammoniacal  salt  comparable  to  ammonium 
tartrate,  or  a  more  complex  compound  analogous  to  pepsin. 
Thus,  the  higher  plant  combines  within  itself  the  two, 
physiologically  distinct,  lower  types  of  the  Fungus  and  the 
Alga. 

That  some  sort  of  circulation  of  fluids  must  take  place 
in  the  body  of  a  plant,  therefore,  appears  to  be  certain,  but 
the  details  of  the  process  are  by  no  means  clear.  There  is 
evidence  to  shew  that  the  ascent  of  fluid  from  the  root  to 
the  leaves  takes  place,  to  a  great  extent,  through  the  elon- 
gated ducts  of  the  wood,  which  not  unfrequently  open  into 
one  another  by  their  applied  ends,  and,  in  that  way,  form 
very  fine  capillary  tubes  of  considerable  length. 


viii.]  THE  BEAN-PLANT.  77 

The  mechanism  by  which  this  ascent  is  effected  is  of  two 
kinds  ;  there  is  a  pull  from  above,  and  there  is  a  push  from 
below.  The  pull  from  above  is  the  evaporation  which  takes 
place  at  the  surface  of  the  plant,  and  especially  in  the  air- 
passages  of  the  leaves,  where  the  thin-walled  cells  of  the 
parenchyma  are  surrounded,  on  almost  all  sides,  with  air, 
which  communicates  directly  with  the  atmosphere  through 
the  stomates.  The  push  from  below  is  the  absorptive  action 
which  takes  place  at  the  extremities  of  the  rootlets,  and 
which,  for  example,  in  a  vine,  before  its  leaves  have  grown 
in  the  spring,  causes  a  rapid  ascent  of  fluid  (sap)  absorbed 
from  the  soil.  A  certain  portion  of  the  fluid  thus  pumped 
up  from  the  roots  to  the  surface  of  the  plant  doubtless 
exudes,  laterally,  through  the  walls  of  the  vessels  (the  thin 
places  which  give  rise  to  the  dots  on  the  walls  of  these 
structures  especially  favouring  this  process),  and,  passing 
from  cell  to  cell,  eventually  reaches  those  which  contain 
chlorophyll.  The  distribution  of  the  compound  containing 
nitrogen  and  carbon,  whatever  it  may  be,  which  is  formed 
in  the  chlorophyll-bearing  cells,  probably  takes  place  by 
slow  diffusion  from  cell  to  cell. 

The  supply  of  air,  containing  carbonic  anhydride,  to  the 
leaves  and  bark  is  effected  by  the  abundant  and  large  air- 
passages  which  exist  between  the  cells  in  those  regions. 
But  it  can  hardly  be  doubted  that  all  the  living  protoplasm 
of  the  plant  undergoes  slow  oxidation,  with  evolution  of 
carbonic  anhydride;  and  that  this  process,  alone,  takes  place 
in  the  deeper-seated  cells.  The  supply  of  oxygen  needful 
for  this  purpose  is  sufficiently  provided  for,  on  the  one  hand, 
by  the  minute  air-passages  which  are  to  be  found  between 
the  cells  in  all  parenchymatous  tissues ;  and  on  the  other,  by 
the  spiral  vessels,  which  appear  always  to  contain  air  under 
normal  circumstances,  in  the  woody  bundles.  The  replace- 


78  ELEMENTARY  BIOLOGY.  [CHAP. 

ment  of  the  oxygen  of  the  air  thus  absorbed,  and  the  re- 
moval of  the  carbonic  anhydride  formed,  will  be  sufficiently 
provided  for  by  gaseous  diffusion. 

From  what  has  been  said,  it  results  that,  in  an  ordinary 
plant,  growing  in  damp  earth  and  exposed  to-  the  sunshine, 
a  current  of  fluid  is  setting  from  the  root  towards  the  surface 
exposed  to  the  air,  where  its  watery  part  is  for  the  most 
part  eva-porated;  while  gaseous  diffusion  takes  place,  in  the 
contrary  direction,  from  the  surface  exposed  to  the  air, 
through  the  air-passages  and  spiral  vessels  which  extend 
from  the  stomates  to  the  radicles  ;  the  balance  of  exchange 
being  in  favour  of  oxygen,  in  all  the  chlorophyll-bearing 
parts  of  the  plant  which  are  reached  by  the  sunlight,  and  in 
favour  of  carbonic  anhydride,  in  its  colourless  and  hidden 
regions.  At  night,  the  evaporation  diminishing  with  the 
lowering  of  the  temperature,  the  ascent  of  liquid  becomes 
very  slow,  or  staps,  and  the  balance  of  exchange  in  the  air- 
passages  is  entirely  in  favour  of  carbonic  anhydride;  even 
the  chlorophyll-bearing  parts  oxydizing,  while  no  carbonic 
anhydride  is  decomposed. 


LABORATORY  WORK, 
a.     General  characters. 

a.  The  erect  central  main  axis  (root  and  stem}. 

b.  The   branches:   some,  mere  repetitions  of  the 
main  axis ;  others,  modified  and  bearing  flowers. 

c.  The  nodes  and  internodes. 

d.  The  appendages. 
a..      Rootlets. 

/?.      Foliage  leaves, 
y.      Floral  leaves. 


VIIL]  THE  BEAN-PLANT.  79 

b.  The  root. 

a.  Its  main  central  portion  (axis). 

b.  The  irregularly  arranged  rootlets  attached  to  the 
axis. 

c.  The  absence  of  chlorophyll  in  the  root. 

d.  The  root-sheath,  covering  the  tip  of  each  rootlet: 
this  is  difficult  to  get  whole  out  of  the  ground  in 
the  bean,  but  is  readily  seen  by  examining  the 
roots  of  duckweed  (Lemna)  with  i  inch  obj.    In 
the  latter  plant  it  consists  of  several  layers  of 
cells  forming  a  cap  on  the  end  of  the  root,  and 
ending  abruptly  with  a  prominent  rim  some  way 
up  it. 

c.  The  stem. 

1 .  Erect,  green,  four-cornered,  with  a  ridge  at  each  angle ; 
not  woody;  the  gradual  shortening  of  the  internodes 
towards  its  apex. 

2.  Cut  a  thin  transverse  section  of  the  stem  through  an 
internode ;  note  its  central  cavity,  and  the  whitish  ring 
of  fibro-vascular  bundles  in  it,   which  is   harder  to 
cut  than  the  rest :  mount  in  water  and  examine  with 
i  inch  obj. :  note — 

a.  The  medullary  or  pith-cavity  in  the  centre  of  the 
section. 

b.  The  pith-cells.,  around  the  central  cavity :  large 
and  more  or  less  rounded  (parenchyma) :  some- 
times with  dotted  walls  from  spots  of  local  thin- 
ness on  them. 

c.  The  epidermis:  composed  of  a  single  layer  of 
somewhat  squarish-looking  cells,  containing  no 
chlorophyll. 


8o  ELEMENTARY  BIOLOGY.  [CHAP. 

d.  Beneath  the  epidermis  several  layers  of  large 
rounded  cells  containing  chlorophyll  (parenchyma 
of  the  bark). 

e.  The  medullary  rays:  radiating  rows  of  paren- 
chymatous  cells  uniting  b  and  d:  not  quite  con- 
tinuous, being  interrupted  by  the  cambium  zone 

(/•  y). 

f.  The  fibre-vascular  bundles^  lying  between  the 
medullary  rays;  commencing  at  the  side  nearest 
the  pith,  note — 

a.  The  large  openings  formed  by  the  transverse 
sections  of  the  spiral  vessels  and  ducts. 

/3.  The  small  thick-walled  wood-cells,  wedged  in 
between  the  vessels.  These  two  (a  and  ft) 
form  the  wood  or  xylem  of  the  bundle.  The 
bast  or  phloem.  It  presents  internally  thin- 
walled  cells  of  various  size,  the  bast  paren- 
chyma and  bast  vessels  or  sieve  tubes.  Ex- 
ternally it  appears  in  cross  section  to  be  com- 
posed of  rounded  cells  with  thickened  walls ; 
the  bast  fibres  or  liber. 

y.  The  cambium  zone:  granular-looking,  and 
composed  of  small  angular  thin-walled  cells. 

8.  The  liber-layer:  in  cross  section  it  seems 
composed  of  rounded  cells  with  much  thick- 
ened walls.  Draw  the  section. 

3.  Cut  a  transverse  section  through  a  node,  and  compare 
it  with  that  through  the  internode. 

4.  Cut  a  thin  longitudinal  section  through  part  of  an 
internode  (if  necessary  the  bit  of  stem  may  be  im- 
bedded in  paraffin  first),   and  mount  it  in  water; 


VIIL]  THE  BEAN-PLANT.  8r 

working  from  the  medullary  cavity  outwards,  note 
the  following  layers,  using  at  first  a  low  power : — 

a.  The  pith-cells :  much  as  in  the  transverse  sec- 
tion. 

b.  The  fibro-vascular  bundles  presenting — 

a.  The  spiral  vessels:  elongated  tubes  with  a  spiral 
thickening  on  their  walls. 

/?.  The  wood-cells:  elongated  and  with  much 
thickened  walls. 

y.  The  dotted  ducts:  much  like  b,  but  the  thick- 
ening not  deposited  in  the  form  of  a  spiral. 

S.  The  cambium  zone:  made  up  of  cloudy- 
looking,  small,  angular,  thin-walled  cells. 

e.  The  bast  parenchyma ;  thin-walled  elongated 
cells. 

£.  The  bast  vessels:  larger  elongated  cells  with 
oblique  perforated  septa  (sieve-tubes). 

77.      The  bast  fibres,  fusiform  and  thick-walled. 

c.  More  parenchymatous  cells. 

d.  Epidermis:    composed    apparently  of   cubical 
colourless  cells :  here  and  there  the  opening  of 
a  stomate  (d.  2.  d.  ft)  may  be  seen. 

Draw  the  section. 

5.  Compare  the  transverse   and  longitudinal   sections 
together,  making  out  the  corresponding  parts  in  each. 

6.  Put  on  a  high  power,  and  examine  each  of  the  above- 
mentioned  tissues  carefully. 

7.  Stain  with  iodine:  note  the  cell-walls ;  fat  protoplasm 
— its  presence  or  absence,  and  relative  quantity  in 
the  various  tissues;   the  nuclei  of  the  cells;  starch 
granules  in  some,  stained  deep  blue  by  the  iodine. 

M.  6 


82  ELEMENTARY  BIOLOGY.  [CHAP. 

d.    The  leaves. 

1.  Their  form  and  composition. 

a.      Each  leaf  consists   of  a  number  of  different 

parts,  viz. : — 
a.      The  stalk  or  petiole. 
P.     The  four  to  six  oval  leaflets  attached  laterally 

to  the  stalk. 
y.      The  pair  of  small  leaf-like  expansions  (stipules) 

at  the  base  of  the  petiole. 

8.  The  rudimentary  tendril  terminating  the  pe- 
tiole. 

2.  The  histological  structure  of  a  leaflet. 

a.  Imbed  a  leaflet  in  paraffin  or  hold  it  between 
two  bits  of  carrot  or  turnip  and  cut  a  thin  sec- 
tion from  it,  perpendicular  to  its  surfaces.     Let 
the  section  lie  in  water  a  few  minutes  to  drive 
the  air  out  of  its  intercellular  spaces,  and  then 
mount  it  in  water,   and  examine  with  i  inch 
objective. 

b.  Begin  at  the  upper  surface  (marked  out  by  its 
more  closely  packed  cells),  and  work  through  to 
the  lower.     Note — 

a.  The  colourless  epidermic  layer — consisting 
of  a  single  row  of  cells;  the  openings  here 
and  there  in  it  (stomatd). 

ft.  Beneath  the  upper  epidermis  come  elongated 
chlorophyll-containing  cells,  set  on  perpendi- 
cularly to  the  surface. 

y.  Then  come  irregularly  branched  (stellate]  cells 
forming  the  lower  half  of  the  leaf-substance ; 
these  also  contain  chlorophyll 


Vin.]  THE  BEAN-PLANT.  83 

S.  The  epidermic  layer  of  the  lower  surface; 
like  a, 

e.  The  intercellular  spaces,  through  the  whole 
thickness  of  the  leaf:  the  direct  communica- 
tion of  some  of  them  with  stomata. 

£.      Here  and  there  sections  of  ribs  or  veins:  make 

out  in  them  the  same  elements  as  in  c.  2./. 
Draw. 

c*  Treat  with  iodine :  make  out  the  sac,  proto- 
plasm (primordial  utricle),  nucleus  and  vacuole 
of  the  cells :  the  starch  granules. 

d.  Peel  off  a  strip  of  epidermis  from  a  leaf  and 
examine  with  a  low  power  :  note — 

a.  The  large  close-fitting  cells,  with  irregularly 
wavy  margins  and  no  chlorophyll,  which 
chiefly  make  up  the  epidermis. 

/?.  The  openings  here  and  there  in  it  '(stomata) ; 
the  two  curved,  chlorophyll-containing  cells 
bounding  each  stomate. 

e.  Gently  pull  a  midrib  in  two  across   its   long 
axis ;  note  the  fine   threads  uniting  the   two 
broken  ends  ;  cut  them  off  with  a  sharp  pair  of 
scissors,   mount   in    water  and   examine   with 
\  or  \  objective  :  they  will  be  found  to  consist 
of  partially  unrolled  spiral  vessels. 

e.     The  flower. 

i.      Its  general  structure. 

a.  Borne  on  a  short  stalk  (peduncle). 

b.  Composed  of  four  rows  or  whorls  of  organs. 
a.      The  external  green  cup-like  calyx, 

6—2 


84  ELEMENTARY  BIOLOGY.  ^       [CHAP. 

P.  Inside  the  calyx  the  corolla:  the  most  con- 
spicuous part  of  the  flower. 

y.      Inside  the  corolla  the  stamens. 
8.      Within  the  stamens  the  pistil. 

2.  The  calyx. 

A  cup  terminated  at  its  free  edge  by  five  prominent 
points,  two  dorsal,  and  three  ventral :  the  five  small 
midribs  running  along  it  (one  to  the  end  of  each  of 
the  points)  represent  the  free  ends  of  five  sepals, 
which  are  united  below. 

3.  The  corolla. 

a.      Composed  of  five  pieces  or  petals. 

a.  On  the  dorsal  side,  a  single  large  piece  (uexil- 
lum)  expanded  at  its  free  end  and  folded  over 
the  rest. 

/3.  On  the  sides,  two  oval  pieces  (al<z),  each 
attached  by  a  distinct  narrowed  stalk  (unguis). 

y.  The  inferior  part  of  the  corolla  (carina\  com- 
posed of  two  oval  pieces  united  along  their 
lower  edge  but  readily  tearing  apart. 

4.  The  stamens. 

a.  Ten  in  number,  each  consisting  of  a  stalk-like 
part,  the  filament,  terminated  by  a  small  knob, 
the  anther.  V . 

b.  The  union  of  the  filaments  for  three-fourths  of 
their  length  to  form  the  stamen-tube :  the  sharp 
bend  of  the  filaments  towards  the  upper  side  at 
the  point  where  they  separate  from  one  another. 

f.      Tease  out  an  anther  in  water  and  examine  with 
•|  obj. :  there  will  be  found  numerous — 


VIIL]  THE  BEAN-PLANT.  85 

a.  Pollen-grains:  small  oval  bodies,  with  pro- 
jections on  them  in  the  equatorial  region. 

d.  The  anther  of  a  bean  is  so  small  that  sections 
cannot  be  made  of  it  without  considerable  skill : 
the  structure  of  an  anther  can  however  be  easily 
made  out  by  imbedding  one  from  a  tiger-lily  in 
paraffin  or  holding  it  between  two  bits  of  carrot, 
cutting  transverse  sections,  mounting  in  water 
and  examining  with  i  inch  obj. 

a.  It  contains  four  chambers,  two  on  each  side 
of  the  continuation  of  the  filament,  and  in 
each  chamber  lie  numerous  pollen-grains. 

5.      The  pistil. 

a.  It  is  found  by  tearing  open  the  stamen-tube  :  it 
is  a  long  green  tapering  body,  somewhat  flat- 
tened laterally  and  ending  in  a  point  (the  style) 
which  bears  a  tuft  of  strong  hairs. 

b.  Slit  it  open  carefully :  in  it  lies  a  central  cavity, 
containing  a  number  of  small  oval  bodies,  the 
ovules,  attached  along  its  ventral  side  by  short 
pedicles. 

c.  It  is  difficult  to  get  a  section  of  a  bean-ovule, 
but  its  essential  structure  may  be  readily  made 
out  by  making  thin  transverse  sections  of  the 
ovary   of  a  large   lily   (where  the   ovules   are 
closely  imbedded  in  a  large  quantity  of  paren- 
chyma) and  examining  with  i  inch  obj. 

a.  The  central  cellular  portion  of  the  ovule 
(nucleus)  made  up  of  a  large  number  of  cells. 

/3.  Its  two  coats,  an  inner  (primine)  and  outer 
(secundine). 


86  ELEMENTARY  BIOLOGY.  [CHAP, 

y.  The  small  passage  (micropyle)  leading  through 
the  coats  down  to  the  nucleus. 

8.  In  some  specimens,  a  large  cavity  (the 
embryo-sac)  will  be  seen  in  the  nucleus  just 
opposite  the  micropyle.  In  the  embryo-sac 
may  be  seen  some  small  granular  cells  (the 
embryo-cell  and  endosperm  cells). 

f.   The  seeds. 

i.  Soak  some  dried  beans  in  water  for  twenty-four 
hours ;  they  will  slightly  swell  up  and  be  more  readily 
examined  than  when  dry. 

a.  Note  the  black  patch  on  one  end  of  the  bean, 
marking  where  the  stalk  (funiculus)  which  fixed 
it  in  the  pod  was  attached  to  it. 

b.  Having  wiped  all  moisture  off  the  bean  gently 
press  it  while  observing  that  part  of  the  black 
patch  which  is  next  its  broader  end  :  close  to 
the  patch  a  minute  drop  of  fluid  will  be  observed 
to  be  pressed  out  through  a  small  opening,  the 
micropyle. 

c.  Carefully  peel  off  the  outer  coat  (testa)  of  the 
seed :  the  two   large  fleshy  cotyledons  will  be 
laid  bare. 

d.  Joining  the  cotyledons  together  will  be  found 
the  rest  of  the  embryo  :  it  consists  of  a  conical 
part  (the  radicle)  lying  outside  the  cotyledons, 
with  its  apex  directed  towards  the  point  where 
the  micropyle  was;  and   of  the  rudiments  of 
the  stem  and  leaves  (plumule)  lying  between 
the  cotyledons. 


viii.]  THE  BEAN-PLANT.  87 

g.    The  process  of  fertilization. 

This  is  difficult  to  follow  in  the  bean;  but  by  using 
different  plants  for  the  observation  of  its  various  stages 
it  is  fairly  easy  to  observe  all  its  more  important  steps. 

1.  A  plant  well  adapted  for  seeing  the  penetration  of 
the   pollen-tube   into   the   stigma  and   style  is   the 
Evening  Primrose  ((Enothera  biennis). 

Detach  the  style  from  the  flower  and  hold  the 
club-shaped  stigma  between  the  finger  and  thumb 
of  the  left  hand.  Moisten  it  with  a  drop  of  water 
and  then  make  with  a  wetted  razor  several  successive 
cuts  throjigh  it.  This  will  divide  the  stigma  into 
several  slices.  Spread  these  out  on  a  glass  slide 
with  a  needle  in  water  and  examine  the  thinnest, 
after  putting  on  a  covering-glass. 

The  triangular  grains  of  pollen  will  be  seen  send- 
ing out  from  one  angle  a  tube  into  the  stigmatic 
tissue,  which  is  easily  seen  from  its  slight  difference 
in  colour. 

2.  The  entrance  of  the  pollen-tube  into  the  micropyle 
can  be  readily  made  out  in  some  species  of  Veronica. 
The  common   V.  serpyllifolia  —  often  to   be   found 
in  shady  places  on  lawns — is  well  adapted  for  the 
purpose.     A  flower  should  be  taken  from  which  the 
corolla  has  just  dropped.      Dissect  out  the  minute 
ovary  and,  using  the  dissecting  microscope,  open 
with  a  needle  one  of  its  two  cells  in  a  drop  of  water; 
remove  the  mass  of  ovules  and  gently  tease  them 
apart.     Then  put  on  a  covering-glass  and  examine 
with  a  low  power  till  an  ovule  is  found  which  shews 
the  entry  of  the  pollen-tube.     The  addition  of  dilute 
glycerine  will  make  the  ovule  more  transparent,  so 


ELEMENTARY  BIOLOGY.  [CHAP.  viu. 

that  after  some  time  the  embryo-sac  can  be  seen, 
and  the  progress  of  the  pollen-tube  into  the  ovule 
followed. 

The  young  fruit  of  Campanula  (especially  the  com- 
mon Canterbury  Bells  of  gardens,  Campanula  me- 
dia] is  convenient  for  examining  the  embryo-sac. 
It  is  only  necessary  to  cut  thin  transverse  sections 
of  the  fruit  and  examine  in  water.  Some  of  the 
ovules  cut  through  will  allow  the  embryo-sac  to  be 
seen,  and  in  fortunate  sections  the  embryo- vesicle 
and  the  end  of  the  pollen-tube  in  contact  with  the 
embryo-sac. 


IX. 
THE   BELL- ANIMALCULE   (Vorticdla\ 

THE  great  majority  of  those  animal  organisms  which  are 
more  complex  than  Amoeba,  begin  their  existence  as  simple 
nucleated  cells,  having  a  general  similarity  to  Amoeba;  and 
the  single  nucleated  cell  which  constitutes  the  whole  animal 
in  its  primitive  condition  divides  and  subdivides  until  an 
aggregation  of  similar  cells  is  formed.  And  it  is  by  the 
differentiation  and  metamorphosis  of  these  primitively  simi- 
lar histological  elements  that  the  organs  and  tissues  of  the 
body  are  built  up.  But  in  one  group,  the  Infusoria,  the 
protoplasmic  mass  which  constitutes  the  germ  does  not 
undergo  this  process  of  preliminary  subdivision,  but  such 
structure  as  the  adult  animal  possesses  is  the  result  of  the 
direct  metamorphosis  of  parts  of  its  protoplasmic  substance. 
Hence,  morphologically,  the  bodies  of  these  animals  are  the 
equivalents  of  a  single  cell;  while,  physiologically,  they  may 
attain  a  considerable  amount  of  complexity. 

The  Infusoria  abound  in  fresh  and  salt  waters,  and  make 
their  appearance  in  infusions  of  many  animal  and  vegetable 
substances,  their  germs  either  being  contained  in  the  sub- 
stances infused,  or  being  wafted  through  the  air.  Their 
diffusion  is  greatly  facilitated  by  the  property  which  many 
of  them  possess  of  being  dried,  and  thus  reduced  to  the 
condition  of  an  excessively  light  dust,  without  the  destruc- 


90  ELEMENTARY  BIOLOGY.  [CHAP. 

tion  of  their  vitality;  while  their  rapid  propagation  is,  in 
the  main,  due  to  their  power  of  multiplying  by  division, 
with  extraordinary  rapidity,  when  duly  supplied  with  nou- 
rishment. The  majority  are  free  and  provided  with  nu- 
merous cilia  by  which  they  are  incessantly  and  actively  pro- 
pelled through  the  medium  in  which  they  live;  but  some 
attach  themselves  to  stones,  plants,  or  even  the  bodies  of 
other  animals.  A  few  are  parasitic,  and  the  bladder  and 
intestines  of  the  Frog  are  usually  inhabited  by  several  spe- 
cies of  large  size. 

The  Bell-animalcules  are  Infusoria  which  are  fixed,  usu- 
ally by  long  stalks,  to  water-plants,  or,  not  unfrequently,  to 
the  limbs  of  aquatic  Crustacea.  The  body  has  the  shape  of 
a  wine-glass  with  a  very  long  and  slender  stem,  provided 
with  a  flattened  disc-like  cover.  What  answers  to  the  rim 
of  the  wine-glass  is  thickened,  somewhat  everted,  and  richly 
ciliated,  and  the  edges  of  the  disc  are  similarly  thickened 
and  ciliated.  Between  the  thickened  edge  of  the  cover,  or 
peristome,  and  the  edge  of  the  disc,  is  a  groove,  which,  at 
one  point,  deepens  and  passes  into  a  wide  depression,  the 
vestibulum.  From  this  a  narrow  tube,  the  oesophagus,  leads 
into  the  central  substance  of  the  body,  and  terminates  ab- 
ruptly therein ;  and  when  faecal  matters  are  discharged,  they 
make  their  way  out  by  an  aperture  which  is  temporarily 
formed  in  the  floor  of  this  vestibule.  The  outermost  layer 
of  the  substance  of  the  body  is  denser  and  more  transparent 
than  the  rest,  forming  a  cuticula.  Immediately  beneath  the 
cuticle  it  is  tolerably  firm  and  slightly  granular,  and  this 
part  is  distinguished  as  the  cortical  layer ;  it  passes  into  the 
central  substance,  which  is  still  softer  and  more  fluid. 

In  the  undisturbed  condition  of  the  Bell-animalcule, 
the  stem  is  completely  straightened  out ;  the  peristome  is 
everted,  and  the  edges  of  the  disc  separated  from  the  peri- 


ix.]  THE  BELL-ANIMALCULE.  9r 

stome;  the  vestibule  gaping  widely  and  the  cilia  working 
vigorously.  But  the  least  shock  causes  the  disc  to  be  re- 
tracted, and  the  edge  of  the  peristome  to  be  curved  in  and 
shut  against  it,  so  as  to  give  the  body  a  more  globular  form. 
At  the  same  time,  the  stem  is  thrown  into  a  spiral,  and  the 
body  is  thus  drawn  back  towards  the  point  of  attachment. 
If  the  disturbing  influence  be  continued,  this  state  of  retrac- 
tion persists ;  but  if  it  be  withdrawn,  the  spirally  coiled  stem 
slowly  straightens,  the  peristome  expands,  and  the  cilia 
resume  their  activity. 

In  the  interior  of  the  body,  immediately  below  the  disc, 
a  space,  occupied  by  a  clear  watery  fluid,  is  seen  to  make 
its  appearance  at  regular  intervals — slowly  enlarging  until 
it  attains  its  full  size,  and  then  suddenly  and  rapidly  dis- 
appearing by  the  approximation  of  its  walls.  This  is  the 
contractile  vesicle.  Whether  it  has  any  communication  with 
the  exterior  or  not  and  what  is  its  function,  are  still  open 
questions.  If  the  Bell-animalcule  is  well  fed,  one  or  more 
watery  vesicles  of  a  spheroidal  form,  each  containing  a  cer- 
tain portion  of  the  ingested  food,  will  be  seen  in  the  soft 
central  mass  of  the  body.  And  by  mixing  a  small  quantity 
of  finely  divided  carmine  or  indigo  with  the  water  in  which 
the  Vorticellce.  live, 'the  manner  in  which  these  food-vesicles 
are  formed  may  be  observed.  The  coloured  particles  are 
driven  into  the  vestibule  by  the  action  of  the  cilia  of  the 
peristome  and  the  adjacent  parts,  and  gradually  accumulate 
at  the  inner  end  of  the  gullet.  After  a  time  the  mass  here 
heaped  together  projects  into  the  central  substance  of  the 
body,  surrounded  by  an  envelope  of  the  accompanying 
water ;  and  then  suddenly  breaks  off,  as  a  spheroidal  drop, 
henceforward  free  in  the  soft  central  substance.  In  some 
Bell-animalcules,  the  food-vesicles  thus  formed  undergo  a 
movement  of  circulation,  passing  up  one  side  of  the  body, 


92  ELEMENTARY  BIOLOGY.  [CHAP. 

then  crossing  over  below  the  disc  and  descending  on  the 
other  side.  Sooner  or  later  the  contents  of  these  vesicles 
are  digested,  and  the  refuse  is  thrown  into  the  vestibule  by 
an  aperture  which  exists  only  at  the  moment  of  extrusion  of 
the  faeces,  and  is  indistinguishable  at  any  other  time. 

A  portion  of  the  substance  of  the  body,  which  is  slightly 
different  in  transparency  and  in  its  reactions  to  colouring 
substances  from  the  rest,  is  called  the  nucleus  or  endoplast. 
It  is  elongated  and  bent  upon  itself  into  a  crescentic  or 
horseshoe  shape. 

The  Bell-animalcules  multiply  in  two  ways;  partly  by 
longitudinal  fission,  when  a  bell  becomes  cloven  down  the 
middle,  each  half  acquiring  the  structure  previously  pos- 
sessed by  the  whole;  and  partly  by  gemmation  from  the 
endoplast,  in  which  latter  case  the  endoplast  divides  and  one 
or  more  of  the  rounded  masses  thus  separated  are  set  free 
as  locomotive  germs. 

Sometimes  a  rounded  body,  encircled  by  a  ring  of  cilia 
but  having  otherwise  the  characters  of  a  Vorticella  bell,  is 
seen  to  be  attached  to  the  base  of  the  bell  of  an  ordinary 
Vorticella.  It  was  formerly  supposed  that  these  were  buds, 
but  it  appears  that  they  are  independent  individuals,  which 
have  attached  themselves  to  that  to  which  they  adhere  and 
are  gradually  becoming  fused  with  it,  so  that  the  two  will 
form  one  indistinguishable  whole.  It  is  probable  that  this 
"  conjugation"  has  relation  to  a  sexual  process. 

Under  certain  circumstances  a  Vorticella  may  become 
encysted.  The  peristome  closes  and  the  bell  becomes  con- 
verted into  a  spheroidal  body,  in  which  only  the  nucleus 
and  the  contractile  vesicle  remain  distinguishable.  This 
surrounds  itself  with  a  structureless  envelope  or  cyst,  from 
which,  after  remaining  at  rest  for  a  longer  or  shorter  time, 
the  Bell-animalcule  may  emerge  and  resume  its  former 


I-X.1  THE  BELL-ANIMALCULE.  93 

state  of  existence.  In  thus  passing  into  a  temporary  condi- 
tion of  rest  many  of  the  other  Infusoria  resemble  Vorticella. 
The  two  genera  of  Infusoria  which  most  commonly  occur 
in  the  Frog  are  Nyctolherus  and  Balantidium.  Both  are 
free  and  actively  locomotive,  and  the  former  is  particularly 
remarkable  for  its  relatively  large  size  and  semilunar  con- 
tour, and  for  the  length  and  distinctness  of  its  curved  oeso- 
phagus. Balantidium  is  pyriform,  and  has  a  very  short 
cesophageal  depression. 


LABORATORY  WORK. 

A.  Examine  duckweed  roots,  confervse,  &c.,  with  \  inch 
objective  avoiding  pressure ;  having  found  a  group  of 
Vorticellce  note  the  following  points  with  a  higher 
power. 

i.    In  the  extended  state  of  the  animal, 
a.     The  body. 

a.  Its  size  (measure). 

b.  Form;  broadly  speaking,  that  of  an  inverted 
bell :  note — 

a.      The  prominent  everted  rim  (peristome). 

P.     The  flattened  central  disc  projecting  above 

the  peristome. 

y.      The  cilia  fringing  the  disc. 
8.      The  depression  between  the  peristome  and 

disc. 
e.       The  mouth  of  the  chamber  (vestibulum)  into 

which  the  oesophagus  and  anus  open,  in  the 

hollow  between  the  peristome  and  disc. 


94  ELEMENTARY  BIOLOGY.  [CHAP. 

c.      Structure. 

a.  The  thin,  transparent,  homogeneous  external 
layer  (cuticle). 

/?.      The  granular  layer  (cortical  layer)  inside  the 
cuticle. 
[Its  fine  transverse  striation.] 

y.  The  central  more  fluid  part,  not  sharply 
marked  off  from  /?. 

The  various  clear  spaces  (alimentary  va- 
cuoles)  in  it,  containing  foreign  (swallowed) 
bodies  (Diatoms,  Protococcus,  &c.). 

8.  The  contractile  vesicle;  its  position,  in  the 
cortical  layer  just  beneath  the  disc;  its  systole 
and  diastole. 

c.  The  nucleus;  an  elongated  curved  body  in 
the  cortical  layer;  sometimes  nearly  homo- 
geneous, sometimes  more  distinctly  granular. 
The  nucleus  is  usually  indistinguishable 
until  after  treatment  with  iodine  (4). 

£.  The  gullet;  sometimes  seen  in  optical  trans- 
verse section  as  a  clear  round  space;  some- 
times seen  sidewise  as  a  canal  opening  above 
on  the  disc,  and  ending  abruptly  below  in  the 
body-substance. 

b.     The  stalk. 

a.      Its  length  and  diameter  (measure). 

/?.  Its  structure ;  the  external  homogeneous  layer 
(sheath)  continuous  with  the  cuticle;  the  highly 
refractive  centre  (axis)  generally  surrounded 
with  granules,  and  continuous  with  the  cor- 
tical layer  of  the  bell. 


ix.]  THE  BELL-ANIMALCULE,  95 

2.  In  the  retracted  state. 

a.  The  body. 

a.  Its  form;  pear-shaped;  rounded  off  above;  no 
disc  or  peristome  visible. 

p.  The  clear  transverse  space  near  the  top,  indi- 
cating the  interval  between  the  retracted  disc 
and  the  rolled-in  peristome.  In  this  space 
the  cilia  can  frequently  be  seen  moving. 

y.      Structure;  as  in  i.  a.  c. 

b.  The  stalk;  thrown  into  corkscrew-like  folds. 

3.  The  movements  of  Vorticella.     Compare  especially 
the  regularity,  definiteness  and  rapidity  of  some  of 
them  with  the   slow  and  irregular  movements    of 
Amoeba.    (III.) 

a.  The  ciliary  movement. 

a.  Examine  the  cilia  carefully;  delicate  homo- 
geneous processes;  their  length,  diameter  and 
form ;  their  position. 

[$.  The  continuity  of  the  cilia  with  the  cortical  layer.] 
y.  The  function  of  the  cilia;  their  rapid  move- 
ments, alternately  bending  and  straightening : 
the  co-ordination  of  these  movements;  they 
work  in  a  definite  order;  note  the  currents 
produced  in  the  neighbouring  water  (if  ne- 
cessary introduce  a  few  particles  of  carmine 
under  the  coverslip);  the  sweeping  of  small 
bodies  down  the  gullet. 

b.  The  movements  of  the  contractile  vesicle  (see  III. 
A.  3.  c).     Tolerably  regular  rhythmic  distension 
and  collapse  (diastole  and  systole). 


$6  ELEMENTARY  BIOLOGY.  [CHAP. 

c.  The  currents  in  the  central  parts  of  the  body  car- 
rying round  the  swallowed  bodies.     (Compare 
VI.  C.) 

d.  The  movements  of  the  animal  as  a  whole.    (J  inch 
or  \  inch  obj.) 

a.  Its  extreme  irritability;  it  contracts  on  the 
slightest  stimulation :  often  without  any  ap- 
parent cause. 

/?.  The  movements  which  occur  in  contraction; 
the  coiling  up  of  the  stalk ;  the  rolling  in  of 
the  disc.  The  rapidity  of  these  movements. 

y.  The  mode  of  re-expansion ;  the  stalk  straightens 
first;  then  the  peristome  is  everted;  finally 
the  disc  and  its  cilia  are  protruded. 

4.  Stain  with  iodine  or  magenta;  the  cuticle  uncoloured 
— the  rest  stained;  the  nucleus  especially  becomes 
deeply  coloured. 

5.  Treat  with  acetic  acid  ;   the  contents  soon  disappear 
(except  perhaps  some  swallowed  bodies) — the  cuticle 
later  or  not  at  alL 

6.  Note  the  following  points  in  various  specimens — 

a.  Multiplication  by  fission  ;  a  bell  partially  divided 
into  two  by  a  vertical  fissure  starting  from  the 
disc. 

P.  Two  complete  bells  on  one  stalk ;  the  result 
of  completion  of  the  fission.  The  development 
of  a  basal  circlet  of  cilia  by  one  or  both  of 
these  bells. 

[y.     Free  swimming  unstalked  bells  (detached  bells 
from  £. 


ix.]  THE  BELL-ANIMALCULE.  97 

[5.  Conjugation;  the  attachment  of  a  small  free 
swimming  bell  to  the  side  of  a  stalked  one.] 

[e.  Ency station;  the  body  contracted  into  a  ball  and 
surrounded  by  a  thickened  structureless  layer, 
the  contractile  vesicle  being  persistently  dilated.] 

B.  Other  forms  closely  allied  to  Vorticella  which  may  be 
met  with,  and  which  will  do  nearly  as  well  for  exami- 
nation, are; — 

a.      Epistylis.    Bell-shaped   animals  growing  on   a 
branched  non-contractile  stalk. 

b.  Carchesium.  A  form  very  like  Vorticella  but  borne 
on  a  branched  contractile  stalk. 

c.  Cothurnia.  An  almost  sessile  form,  provided  with 
a  cup  or  envelope  into  which  the  bell  can  be  re- 
tracted. 

[The  activity  of  the  movements  of  the  free  Infusoria  inter- 
feres with  the  complete  examination  of  the  living  animal.  It  is 
well  therefore  to  add  a  little  osmic  acid  solution  to  the  drop  of 
water  under  examination.  This  kills  such  Infusoria  as  Para- 
mcecium,  Nyctotherus  and  Balantidium  instantly,  without  de- 
stroying the  essential  features  of  their  organization.] 


THE   FRESHWATER    POLYPES    (Hydra   viridis 
and  H.  fused). 

IF  a  waterweed,  such  as  duckweed,  from  a  pond,  is  placed 
in  a  glass  and  allowed  to  remain  undisturbed  for  a  short  time, 
minute  gelatinous-looking  bodies  of  a  brownish  or  green 
colour  may  frequently  be  found  attached  to  it,  or  to  the  sides 
of  the  glass.  They  have  a  length  of  from  \  to  J  of  an  inch, 
and  are  cylindrical  or  slightly  conical  in  form.  From  the 
free  end  numerous  delicate  filaments,  which  are  often  much 
longer  than  the  body,  proceed  and  spread  out  with  a  more 
or  less  downward  curve,  in  the  water.  If  touched,  these 
threads,  which  are  the  tentacles,  rapidly  shorten  and  together 
with  the  body  shrink  into  a  rounded  mass.  After  a  while, 
the  contracted  body  and  the  tentacles  elongate  and  resume 
their  previous  form.  These  are  Polypes,  the  brown  ones 
belonging  to  the  species  termed  Hydra  fusca,  the  green 
to  that  called  H.  viridis.  The  polypes  usually  remain  at- 
tached to  one  spot  for  a  long  time,  but  they  are  capable 
of  crawling  about  by  a  motion  similar  to  that  of  the  looping 
caterpillar;  and,  sometimes,  they  detach  themselves  and  float 
passively  in  the  water. 

When  any  small  animal,  such  as  a  water-flea,  swimming 
through  the  water  comes  in  contact  with  the  tentacles',  it  is 
grasped,  and  conveyed  by  their  contraction  to  the  aperture 


CHAP,  x.]         THE  FRESH-WATER  POLYPES.  99 

of  the  wide  mouth,  which  is  situated  in  the  middle  of  the 
circle  formed  by  the  bases  of  the  tentacles.  It  is  then 
taken  into  a  cavity  which  occupies  the  whole  interior  of  the 
body;  the  nutritive  matters  which  it  contains  are  dissolved 
out  and  absorbed  by  the  substance  of  the  Hydra;  and  the 
innutritions  residuum  is  eventually  cast  out  by  the  way  it 
entered.  Small  pieces  of  meat,  brought  within  reach  of 
the  tentacles,  are  seized,  swallowed  and  digested  in  the  same 
manner. 

If  a  Hydra  is  well  fed,  bud-like  projections  make  their 
appearance  upon  the  outer  surface  of  the  body.  These 
gradually  elongate  and  become  pear-shaped.  At  the  free 
end  a  mouth  is  formed ;  and  around  it  minute  processes  are 
developed  and  grow  into  tentacles;  and  thus  a  young  Hydra 
is  formed  by  gemmation  from  the  parent.  This  young  Hydra 
becomes  detached  sooner  or  later,  and  leads  an  independent 
existence;  but,  not  unfrequently,  new  buds  are  developed 
from  other  parts  of  the  parent  before  the  first  is  detached, 
and  the  progeny  may  themselves  begin  to  bud  before  they 
attain  independence.  In  this  manner,  temporarily  compound 
organisms  may  be  formed.  Experiments  have  shewn  that 
these  animals  may  be  cut  into  halves  or  quarters  and  that 
each  portion  will  repair  its  losses,  and  grow  up  into  a  perfect 
Hydra;  and  there  is  reason  to  believe  that  this  process 
of  fission  sometimes  occurs  naturally. 

The  Hydra  multiplies  by  budding  through  the  greater 
part  of  the  year;  but  in  the  summer  projections  of  the  surface 
appear  at  the  bases  of  the  tentacles  or  nearer  the  attached 
end  of  the  body.  Within  the  former  (testes)  great  numbers 
of  minute  particles,  each  moved  by  a  vibratile  cilium,  are 
developed  and  are  eventually  set  free.  Functionally,  these 
answer  to  the  antherozooids  of  plants,  and  they  are  termed 
spermatozoa. 

7—2 


ioo  ELEMENTARY  BIOLOGY.  [CHAP. 

The  enlargement  formed  near  the  attached  end  of  the 
polype  may  be  single,  as  in  Hydra  viridis,  or  as  many  as 
eight  may  be  found  in  other  species.  It  becomes  much  larger 
than  the  testis,  and  is  the-  ovary.  Within  it  is  developed 
a  single  large  egg,  or  ovum.  This  ovum,  which  is  a  huge 
nucleated  cell,  is  impregnated  by  the  spermatozoa  and 
undergoes  division  into  two  parts.  Each  of  these  again 
divides  into  two ;  and  so  on,  until  the  ovum  is  broken  up 
into  a  number  of  small  embryo-cells.  The  mass  of  embryo- 
cells  thus  formed  becomes  surrounded  with  a  thick,  usually 
tuberculated  or  spinous,  case;  and,  detaching  itself  from 
the  body,  forms  the  'egg,'  from  which  a  new  Hydra  is  de- 
veloped. 

Microscopic  examination  shews  that  the  body  of  the 
Hydra  is  a  sac,  the  wall  of  which  is  composed  of  two 
membranes,  an  outer  (ectoderm},  and  an  inner  (endoderm). 
The  tentacles  are  tubular  processes  of  the  sac,  and  therefore 
are  formed  externally  by  the  ectoderm  and  lined  internally 
by  the  endoderm.  Both  the  endoderm  and  the  ectoderm 
are  made  up  of  nucleated  cells ;  the  inner  ends  of  those 
of  the  ectoderm  being  prolonged  into  delicate  fibres,  which 
run  parallel  with  the  long  axis  of  the  body  on  the  inner  face 
of  the  ectoderm.  The  green  colour  of  the  Hydra  viridis 
results  from  the  presence  of  chlorophyll  grains  imbedded  in 
the  protoplasm  of  the  cells. 

In  both  the  ectoderm  and  the  endoderm  the  protoplasm 
of  the  cells  contains  very  singular  bodies, — the  so-called 
urticating  capsules,  thread-cells,  or  nematocysts — which  are 
oval  bags,  with  thick  and  elastic  walls,  containing  a  spirally 
coiled-up  filament  which  is  unrolled  suddenly  on  the 
slightest  pressure,  and  then  presents  the  appearance  of  a  long 
filament  attached  to  the  capsule,  and  often  provided  with 
three  recurved  spines  near  its  base.  As  similar  capsules  of 


X.]  THE  FRESH-WATER  POLYPES.  iot 

a  larger  size  are  the  agents  by  which  many  of  the  jelly  fishes 
sting  severely,  just  as  nettles  do  when  they  are  handled,  there 
is  every  reason  to  believe  that  the  thread-cells  of  the  Hydra 
exert  a  like  noxious  influence  upon  the  small  animals  which 
serve  as  their  prey. 

Thus,  Hydra  is  essentially  a  cellular  organism  like  one 
of  the  lower  plants,  but  differs  from  them  morphologically 
in  the  fact  that  its  cells  are  not  enclosed  within  cellulose 
walls ;  and  physiologically,  in  the  dependence  of  these  cells 
for  their  nutrition  upon  ready  formed  protein  matter.  The 
function  of  the  chlorophyll  granules  contained  in  the  endo- 
derm  of  the  green  Hydra,  and  of  the  brown  or  orange- 
coloured  particles  in  the  endoderm  of  the  other  species,  is 
wholly  unknown. 

The  Hydra,  again,  may  be  compared  to  an  aggregate  of 
Amoeba,  which  are  arranged  in  the  form  of  a  double-walled 
sac  and  have  undergone  a  certain  amount  of  metamorphosis. 

It  is  possible  that  the  longitudinal  fibres  connected  with 
the  cells  of  the  ectoderm  may  be  specially  contractile,  and 
represent  muscles ;  but,  however  this  may  be,  each  cell  has 
its  own  independent  contractility.  No  trace  of  a  special 
nervous  system  has  yet  been  discovered,  and  the  manner  in 
which  the  actions  of  the  different  parts  of  the  Hydra  are 
combined  to  a  common  end,  as  in  locomotion  and  the  seizing 
of  prey,  is  not  understood. 

The  Hydra  has  none  of  the  special  apparatuses  which  are 
termed  sense-organs,  or  glands.  The  cavity  of  the  body 
alone  represents  a  stomach  and  intestine;  there  are  no 
organs  of  circulation,  respiration  or  urinary  secretion;  the 
products  of  digestion  being  doubtless  transmitted,  by  im- 
bibition, from  cell  to  cell,  and  those  of  fhe  waste  of  the  cells 
exuded  directly  into  the  surrounding  water. 


102  ELEMENTARY  BIOLOGY.  [CHAP. 

LABORATORY  WORK. 

1.  Put  into  a  beaker  some  water  containing  bodies  to 
which  Hydrae  are  attached,  and  place  the  beaker  in  a 
window  not  exposed  to  direct  sunlight :  in  the  course 
of  some  hours  many  Hydrae  will  be  found  attached 
to  that  side  of  the  glass  which  is  turned  towards  the 
light.     Note  their  size,  form,  colour,  mode  of  attach- 
ment and  movements. 

2.  Transfer  a  Hydra,  by  means  of  a  pipette,  on  to  a 
slide ;  cover  in  plenty  of  water  with  a  large  coverslip, 
and  examine  with  i  inch  obj.     Note — 

a     Form. 

a.  The  base  (so  called  foot) :  a  flattened  disc  :  nar- 
rower or  wider  than  the  body  according  to  the 
state  of  extension  of  the  latter. 

,/3.  The  .body  prcper:  cylindrical,  varying  much  in 
length  and  diameter  with  the  state  of  extension 
>of  the  animal;  its  conical  free  end,  with  an  open- 
ing (mouth)  in  it.  It  is  often  difficult  to  see  the 
mouth  in  this  way,  especially  in  the  green  species. 
It  is  readily  seen  however  if  a  Hydra  be  placed 
in  a  drop  of  water,  without  a  coverslip,  and  be 
watched  with  an  inch  objective  until  it  turns  its 
anterior  end  up  towards  the  observer. 

y.  The '  tentacks:  ranged  round  the  mouth;  then 
number  and  shape;  their  varying  length  and 
diameter ;  the  knob-like  eminences  on  them. 

S.  The  iestes:  small  conical  colourless  eminences  be- 
low the  point  of  attachment  of  the  tentacles. 


x.]  THE  FRESH-WATER  POLYPES.  103 

e.  The  ovary:  a  larger  rounded  colourless  pro- 
minence near  the  base  :  there  may  be  more  than 
one. 

£.  The  buds:  young  Hydrae,  of  various  sizes  and 
stages  of  development,  attached  to  the  sides  of 
the  parent. 

Either  8,  e,  or  £,  or  all  of  them,  may  be  absent  in 
some  specimens. 

b.  Structure. 

a.  The  animal  evidently  composed  of  two  layers, 
an  outer,  ectoderm,  and  inner,  endoderm,  the  latter 
alone  containing  chlorophyll  in  the  green  species : 
the  ectoderm  is  marked  out  into  areas,  and  may 
with  care  be  seen  to  be  composed  of  distinct 
cells,  though  this  is  a  little  difficult  to  make  out 
in  fresh  specimens. 

P.  The  body -cavity:  difficult  to  make  out  in  the 
green  species,  frequently  visible  in  the  brown 
ones  as  a  darker  central  patch  with  which  the 
mouth-opening  is  continuous;  the  extension  of 
the  body-cavity  into  the  tentacles.  Note  cor- 
puscles floating  along  inside  them  when  they  are 
extended. 

c.  Movements. 

a.  The  general  contractility  of  the  animal ;  it  is  con- 
stantly either  extending  or  shortening  its  body 
and  tentacles,  and  so  altering  its  form  and  place. 

/?.  Its  irritability ;  slight  pressure  or  other  stimulus 
immediately  causes  it  to  contract. 

3.     Examine  with  a  high  power:  try  to  make  out  the 
different  cells  of  the  ectoderm — 


104  ELEMENTARY  BIOLOGY.  [CHAP. 

a.  Large  somewhat  conical  nucleated  cells,  with  the 
broader  end  turned  outwards. 

ft.  Smaller  rounded  cells  packed  between  the  deep 
ends  of  the  larger  ones. 

y.  The  nematocysts:  small  oval  capsules,  with  a  fila- 
ment coiled  up  inside  them,  which  are  dispersed 
through  the  ectoderm  in  the  interior  of  its  com- 
ponent cells. 

4.  Treat  with  magenta :  note  the  staining  of  the  cells, 
the  emission  of  the  thread-cells,  and  the  protrusion  of 
their  threads  :  three  chief  forms  of  thread-cell — 

a.  An  oval  capsule  with  a  filament  many  times  its 
own  length  attached  to  one  end,  and  three  short 
processes  radiating  from  the  base  of  the  thread. 

P.  Smaller  thread-cells,  without  the  radiating  pro- 
cesses and  with  a  short  thread. 

y.      Cells  like  /?,  but  with  a  much  longer  thread. 

5.  Imbed  in  paraffin  a  Hydra  which  has  been  hardened 
in  chromic  or  osmic  acid 1  and  cut  sections  from  it ; 
or  lay  a  prepared  Hydra  on  a  glass  slide  and  with 
a  razor  cut  off  transverse  slices ;  having  obtained  by 
either  method  a  number  of  thin  sections  mount  them 
in  glycerine  and  make  out — 

a.  The  large  and  small  cells  of  the  ectoderm  and  its 
thread-cells,  their  arrangement  and  relations.  (3). 

1  When  a  Hydra  is  placed  in  the  above  hardening  fluids  it  nearly 
always  contracts  so  much  as  to  make  it  difficult  to  cut  sections.  If  it  be 
first  killed,  by  placing  it  in  a  small  quantity  of  water  and  when  it  has 
expanded  adding  some  boiling  water,  fairly  extended  specimens  for 
hardening  can  usually  be  obtained. 


x.]  THE  FRESH-WATER  POLYPES.  105 

ft  The  cells  of  the  endoderm :  large,  nucleated,  with 
a  flattened  base  and  a  rounded  free  end :  their 
arrangement  in  a  single  layer. 

y.  The  thin  intermediate  layer  (muscular  stratum} 
between  ectoderm  and  endoderm. 

8.    The  body  cavity. 

6.  Tease  out  in  water  a  specimen  which  has  been 
treated  with  weak  chromic  acid  (o.  ig)  or  with  osinic 
acid :  make  out  the  various  cells  already  described  : 
notice  branched  tails  proceeding  from  the  narrower 
ends  of  the  larger  ectoderm  cells. 

[7.  Tease  out  a  fresh  Hydra  in  water  and  observe  the 
various  cells.  Note  the  amoeboid  movements  exhibited 
by  some,  and  the  single  cilium  attached  to  other  (endo- 
derm) cells.] 

3.  Gently  flatten  out  a  testis  in  water  by  pressure  on  the 
coverslip,  and  examine  with  a  high  power.  Accord- 
ing to  its  state  of  maturity  the  following  contents  will 
be  found  in  it — 

a.    A  collection  of  the  smaller  ectoderm  cells. 

(3.  The  same  but  having  lost  their  nucleus  and 
become  hyaline. 

y.  Cells  otherwise  like  ft  but  with  a  long  filament 
proceeding  from  them. 

B.  Ripe  spermatozoa:  bodies  consisting  of  a  very 
small  oval  head  to  which  a  very  delicate  filament 
is  attached,  and  which,  should  they  get  free,  swim 
about  in  the  water  by  the  movements  of  this  fila- 
ment. They  may  frequently  be  seen  in  motion 
within  the  unruptured  testis. 


106  ELEMENTARY  BIOLOGY.  [CHAP.  x. 

9.      Press  out  an  ovary:  according  to  its  stage  of  develop- 
ment there  will  be  found  in  it — 

a.  Simply  ectoderm  cells  with  an  unusual  prepon- 
derance of  the  smaller  form. 

ft.  Imbedded  among  cells  like  a,  one  which  has 
become  larger  and  clearer  than  the  rest,  and 
possesses  a  distinct  central  clear  spot  in  it. 

y.  Considerable  aggregation  of  granular  proto- 
plasm round  this  cell,  so  as  to  form  a  body 
consisting  of  a  granular  protoplasmic  mass,  in 
which  is  imbedded  a  clear  round  vesicle,  which 
again  contains  a  distinct  rounded  dot. 

8.  The  ripe  ovum.  Consisting  of  a  great  irregu- 
larly branched  mass  of  protoplasm  (vitellus), 
in  which  is  a  clear  space  (germinal  vesicle) 
containing  another  body  (the  germinal  spot).  . 

^  e.  The  segmented  ovum:  composed  of  a  large 
number  of  small  cells.  Its  thick  capsule, 
rough  on  its  external  surface. 


XI. 

THE   FRESH-WATER   MUSSEL 

(Anodonta  Cygnaa). 

UNDER  the  name  of  'Fresh-water  Mussel'  two  distinct  kinds 
of  animals,  which  are  not  unfrequently  abundant  in  our  ponds 
and  rivers,  are  included;  namely,  the  Anadonta  and  two  or 
three  kinds  of  Unio.  The  Anodonta  is  chosen  for  special 
study  here,  but  what  is  said  about  it  applies  very  well  to  all 
parts  of  Unio  except  the  shell. 

The  animal  is  enclosed  in  a  shell  composed  of  two  pieces 
or  valves,  which  are  lateral,  or  right  and  left,  in  relation  to 
the  median  plane  of  the  body.  The  more  rounded  and 
broader  end  is  anterior,  the  more  tapering,  posterior.  If 
placed  in  a  vessel  of  water,  at  the  bottom  of  which  there  is  a 
tolerably  thick  layer  of  soft  mud  or  sand,  and  left  quite  un- 
disturbed, the  Anodonta  will  partially  bury  itself  with  its  an- 
terior end  directed  obliquely  downwards;  and  the  valves  will 
separate  at  their  ventral  edges  for  a  short  distance.  At  the 
edges  of  this  '  gape'  of  the  shell  the  thickened  margins  of  a 
part  of  the  contained  body  which  is  called  the  mantle,  be- 
come visible,  and  between  them  a  large,  whitish,  fleshy, 
tongue-shaped  structure — the  foot — not  unfrequently  pro- 
trudes, and  is  used  to  perform  the  sluggish  movements  of 
which  the  Anodonta  is  capable.  If  some  finely  dividing 
colouring  matter,  such  as  indigo,  is  dropped  into  the  water, 


ro8  ELEMENTARY  BIOLOGY.  [CHAP. 

so  as  to  fall  towards  the  gape,  it  will  be  seen  to  be  sucked 
in;  while,  after  a  short  time,  a  current  of  the  same  substance 
will  flow  out  from  an  opening  between  the  two  edges  of  the 
mantle  on  the  dorsal  side  of  the  posterior  end  of  the  body ; 
and  these  'inhalent'  and  'exhalent'  currents  go  on,  so  long 
as  the  animal  is  alive  and  the  valves  are  open.  Any  disturb- 
ance, however,  causes  the  foot,  if  it  was  previously  protruded, 
to  be  retracted,  while  the  edges  of  the  mantle  are  drawn  in 
and  the  two  valves  shut  with  great  force.  On  the  other 
hand,  in  a  dead  Anodonta  the  valves  always  gape,  and  if 
they  are  forcibly  shut  spring  open  again.  The  reason  of  this 
is  the  presence  of  an  elastic  band,  which  unites  the  dorsal 
margins  of  the  two  valves,  for  some  distance,  and  is  put  on 
the  stretch  when  the  valves  are  forcibly  brought  together. 
During  life  they  are  thus  addncted  by  the  contraction  of  two 
thick  bundles  of  muscular  fibres,  which  pass  from  the  inner 
face  of  one  valve  to  that  of  the  other,  one  at  the  anterior 
and  the  other  at  the  posterior  end  of  the  body,  and  are  called 
the  anterior  and  posterior  adductors. 

The  animal  can  be  extracted  from  the  shell  without 
damage,  only  by  cutting  through  these  muscles  close  to  their 
attachments.  It  is  bilaterally  symmetrical,  the  foot  pro- 
ceeding from  the  middle  of  its  ventral  surface ;  the  mouth  is 
median  and  situated  between  a  projection,  which  answers  to 
the  under  surface  of  the  anterior  adductor  muscle,  and  the 
superior  attachment  of  the  foot.  On  each  side  of  the  mouth 
are  two  triangular  flaps  with  free  pointed  ends — the  labial 
palpi — and  behind  these,  on  each  side,  two  broad,  plate-like 
organs,  with  vertically  striated  outer  surfaces,  are  visible. 
These  are  the  gills  or  branchia.  In  the  dorsal  region,  the 
integument  is  soft  and  smooth ;  on  each  side,  it  is  produced 
into  large  folds,  the  lobes  of  the  mantle  or  pallium,  which 
closely  adhere  to  the  inner  surface  of  the  valves  of  the  shell, 


XL]  THE  FRESH-WATER  MUSSEL.  109 

and  end,  ventrally,  in  the  thickened  margins  already  men- 
tioned. They  pass  into  one  another  in  front  of  the  mouth ; 
at  the  sides,  they  are  united  with  the  dorsal  edges  of  the 
outer  gill-plates;  and,  behind,  they  extend  upwards  and  on 
to  the  dorsal  face  of  the  body,  before  finally  passing  into  one 
another  above,  and  in  front  of,  the  anus,  which  is  small, 
tubular,  prominent,  and  median.  Thus  the  anus  is  inclosed 
in  a  part  of  the  cavity  bounded  by  the  two  mantle  lobes, 
which  is  relatively  small  and  shallow,  and  is  termed  the  doacal 
chamber;  while  the  gills,  the  foot,  and  the  palps,  hang  down 
into  the  relatively  large  branchial  chamber  which  occupies 
the  space  between  the  mantle-lobes  for  the  rest  of  their 
extent.  It  is  the  prolongation  of  the  margins  of  the  former 
cavity  which  gives  rise  to  the  tubular  anal  siphon  seen  in  so 
many  Lamellibranchs ;  while  the  ventral  or  branchial  siphon 
is  a  similar  prolongation  of  the  margins  of  the  branchial 
chamber.  The  dorsal  siphon  is  the  channel  through  which 
the  exhalent  currents  pass ;  the  ventral,  that  for  the  inhalent 
currents. 

The  currents  are  produced  and  kept  up  by  the  action  of 
the  cilia  which  abound  upon  the  gills.  The  latter  are  per- 
forated by  innumerable  small  apertures,  and  the  chambers 
contained  between  the  two  lamellae  of  which  each  gill  is 
formed,  are  in  communication,  above,  with  the  cloacal 
chamber.  The  cilia  work  in  such  a  way  as  to  drive  the 
water  in  which  the  animal  lives  from  the  outer  surface  of 
each  gill  towards  its  interior.  Hence  the  current  which  sets 
from  the  branchial  to  the  cloacal  chamber. 

The  current  of  water  which  is  thus  continually  drawn  into 
the  branchial  chamber  carries  with  it  minute  organisms,  In- 
fusoria, Diatoms  and  the  like,  and  many  of  these  are  swept 
to  the  fore  part  of  the  branchial  chamber,  where  they  enter 
the  mouth,  and  are  propelled  by  the  cilia  which  line  its  cavity 


no'  ELEMENTAR  Y  BIOL  OGY.  [CHAP. 

into  the  alimentary  canal.  The  latter  presents  a  short  and 
wide  gullet,  a  stomach  surrounded  by  hepatic  follicles,  a  long 
intestine  coiled  upon  itself,  in  a  somewhat  complicated 
•manner,  and,  finally,  a  rectum,  which  lies  in  the  middle  line 
of  the  dorsal  aspect  of  the  body,  traverses  the  pericardium 
and  the  heart  which  lies  therein,  and  finally  ends  in  the 
anus. 

As  the  mouth^  is  below  and  behind  the  anterior  adductor 
and  the  rectum  passes  in  front  of  and  above  the  posterior 
adductor,  it  is  clear  that  the  alimentary  canal,  as  a  whole, 
lies  between  the  two  adductor  muscles. 

Digestion,  that  is  solution  of  the  proteinaceous  and  other 
nutritive  matters  contained  in  food,  is  effected  in  the  sto- 
mach and  intestine ;  and  the  nutritious  fluid,  thus  formed, 
transudes  through  the  walls  of  the  alimentary  cavity  and 
passes  into  the  blood  contained  in  the  blood-vessels  which 
surround  it.  This  blood  is  thence  carried  into  a  large  sinus, 
which  occupies  the  middle  line  of  the  body  under  the  peri- 
cardium and  between  the  organs  of  Bojanus  (see  Laboratory 
Work  5),  and  receives  the  greater  part  of  the  blood  return- 
ing from  all  parts  of  the  body.  From  this  median  vena  cava, 
branches  are  given  off  to  the  gills  and  open  into  the  exten- 
sive vascular  network  which  those  organs  contain.  From 
this,  again,  trunks  lead  towards  the  pericardium  and  open 
into  one  or  other  of  the  two  auricles  of  the  heart,  which 
communicate  by  valvular  apertures  with  the  ventricle.  The 
ventricle  gives  off  two  aortic  trunks,  one  of  which,  the  ante- 
rior, runs  forwards  in  the  middle  line,  above  the  rectum, 
while  the  other  runs  backwards,  below  the  rectum.  From 
these  two  aortas  branches  are  given  off  which  divide  into 
smaller  ramifications  for  the  different  regions  of  the  body, 
and  for  the  viscera,  and  finally  terminate  in  channels  which 
answer  to  the  capillaries  of  the  higher  animals. 


xr.]  THE  FRESH-WATER  MUSSEL.  m 

The  pericardial  cavity,  in  which  the  heart  is  lodged,  is 
situated  in  the  posterior  half  of  the  dorsal  region  of  the 
body.  Through  its  thin  dorsal  wall,  and,  still  better,  when 
it  is  carefully  laid  open,  the  heart  can  be  seen  beating.  The 
auricles  contract,  and,  after  them,  the  ventricle ;  the  wave- 
like  contraction  of  the  latter  being  much  the  more  easily 
visible.  The  lips  of  the  auriculo-ventricular  apertures  are  so 
disposed  that  the  blood  is  impeded  from  flowing  back  into 
the  auricles,  when  the  ventricles  contract,  and  is  forced  out, 
either  forwards  or  backwards,  through  the  two  aortae.  From 
these  it  finds  its  way  to  the  capillaries,  and  returns  from  them 
to  the  vena  cava;  whence  it  is  carried,  through  the  organs  of 
Bojanus,  to  the  branchiae.  Here  it  becomes  purified  of  car- 
bonic anhydride,  and  receives  oxygen  from  the  water  in 
which  the  branchiae  are  plunged ;  and  it  is  finally  brought 
back  in  an  arterialized  condition  to  the  heart. 

The  heart  is  therefore  systemic  and  propels  aerated 
blood. 

The  majority  of  the  vessels  which  convey  the  blood  from 
the  vena  cava  to  the  branchiae,  traverse  the  walls  of  the 
dark-coloured  organs — the  organs  of  Bojanus — which  has 
already  been  mentioned ;  and  it  is  probable  that  they  here 
part  with  their  nitrogenous  waste  matters — the  organ  of 
Bojanus,  in  all  probability,  playing  the  part  of  a  kidney. 
The  cavity  of  the  organ  of  Bojanus  communicates,  on  the 
one  hand,  with  the  pericardium,  and,  on  the  other,  with  the 
exterior,  by  an  aperture  which  is  situated  close  to  the  attach- 
ment of  the  inner  gill  to  the  walls  of  the  body.  Thus  the 
cavity  of  the  pericardium  communicates  directly  with  the 
exterior,  though  by  a  roundabout  way.  But  it  also  com- 
municates directly  with  the  venous  system,  by  sundry  small' 
apertures  placed  in  the  anterior  part  of  its  floor.  Hence 
it  must  contain  a  mixture  of  blood  and  water. 


ii2  ELEMENTARY  BIOLOGY.  [CHAP. 

The  blood  of  the  Anoddnta  is  colourless,  and  contains 
colourless  corpuscles,  which  resemble  those  of  Man  in  struc- 
ture and  present  the  same  Amcebiform  movements. 

The  nervous  system  of  the  Anadonta  consists  of  three 
pairs  of  yellow  ganglia ;  the  cephalic,  situated  at  the  sides  of 
the  mouth ;  the  pedal,  placed  in  the  foot ;  and  the  parieto- 
splanchnic,  on  the  under  face  of  the  posterior  adductor  mus- 
cle. They  are  united  by  commissural  cords  which  connect 
the  cephalic  ganglia  with  one  another,  and  with  the  pedal 
and  parieto-splanchnic  ganglia,  respectively.  The  only  sense 
organs  which  have  been  discovered,  are  a  pair  of  auditory 
vesicles,  connected  by  nervous  cords  with  the  pedal  ganglia. 

The  sexes  are  distinct.  The  testes  and  ovaria  are  similar 
in  character,  being  racemose  glands,  which,  in  the  breeding 
season,  occupy  a  great  part  of  the  interior  of  the  body. 
There  is  one  gland  on  each  side,  opening  by  a  minute  aper- 
ture close  to  that  of  the  organ  of  Bojanus. 

The  spermatozoa  have  minute,  short,  rod-like  bodies,  to 
which  a  long,  filamentous,  active  cilium  is  attached,  and, 
thrown  off  in  enormous  numbers,  make  their  way  out  with 
the  exhalent  currents. 

The  ova  are  spherical,  and  the  vitelline  membrane  is  pro- 
duced at  one  point  into  a  short  open  spout-like  tube,  with  a 
terminal  aperture,  the  micropyle,  through  which,  in  all  pro- 
bability, the  spermatozoon  makes  its  entrance.  When  fully 
formed,  multitudes  of  these  ova  pass  out  of  the  oviducal 
aperture  and  become  lodged  in  the  chambers  of  the  gills, 
particularly  the  external  gill,  which  is  frequently  completely 
distended  by  them.  Here  they  are  hatched,  and  give  rise  to 
embryos,  which  are  so  wholly  unlike  the  parent  Anodonta, 
that  they  were  formerly  thought  to  be  parasites,  and  received 
the  name  of  Glochidium.  The  embryo  Anodonta  is  provided 
with  a  bivalve  shell.  Each  valve  has  the  form  of  an  equi- 


XL]  THE  FRESH-WATER  MUSSEL.  113 

lateral  triangle  united  by  its  base  with  its  fellow,  by  means 
of  an  elastic  hinge,  which  tends  to  keep  the  two  wide  open. 
The  apex  of  the  triangle  is  sharply  incurved,  and  is  produced 
into  a  strong  serrated  tooth,  so  that  when  the  valves  ap- 
proach, these  teeth  are  directed  towards  one  another.  The 
mantle  is  very  thin,  and  the  inner  surface  of  each  of  its  lobes 
presents  three  papillae,  terminated  by  fine  pencils  of  hair- 
like  filaments.  What  appears  to  be  the  oral  aperture  is  wide, 
and  its  margins  are  richly  ciliated.  There  is  a  single  ad- 
ductor muscle  and  a  rudimentary  foot,  from  which  one  or 
two  long  structureless  filaments,  representing  the  byssus  of 
the  sea-mussel,  proceed.  These  byssal  filaments  become 
entangled  with  one  another  and  tend  to  keep  the  '  Glochi- 
dia '  in  their  places. 

After  a  time  the  larval  Anodontcz  leave  the  body  of  the 
parent,  and  attach  themselves  to  floating  bodies — very  com- 
monly to  the  tails  of  fishes — by  digging  the  incurved  points 
of  their  valves  into  the  integument  in  the  latter  case,  and 
holding  on  by  them  as  if  they  were  pincers.  In  this  situa- 
tion they  undergo  a  metamorphosis;  the  gills  are  developed, 
the  foot  grows,  the  auditory  vesicles  become  conspicuous  in 
it,  and  the  young  Anodonta  at  length  drops  off  and  falls  into 
its  ordinary  habitation  in  the  mud. 


LABORATORY  WORK. 

i.  In  the  natural  state  of  the  animal  only  the  shell  or 
exoskeleton  is  visible,  or  this  may  be  slightly  open, 
and  then  the  edge  of  the  membrane  lining  it  (the 
mantle]  may  be  visible.  Raise  one  valve  of  the  shell, 
by  separating  the  mantle  from  it  with  the  handle  of  a 
scalpel,  and  then  cutting  through  two  strong  bodies 

3 


ii4  ELEMENTARY  BIOLOGY.  [CHAP. 

(the  adductor  muscles),  one  at  each  end  of  the  animal, 
which  run  from  one  valve  of  the  shell  to  the  other 
and  prevent  their  separation.  The  two  valves  will 
now  be  united  only  by  their  ligament. 

2.    General  form  and  structure. 

a.  In    the   animal    now   laid  bare    may   be  distin- 
guished— 

a.      A  dorsal  border  turned  towards  the  hinge  of 
the  shell,  and  nearly  straight. 

(3.  A  curved  ventral  border,  opposite  the  dorsal, 

y.  A  wider  anterior  end. 

8.  A  narrower  posterior  end. 

c.  A  right  and  left  side. 

b.  The  mantle  or  pallium. 

a.  A  bilobed  semitransparent  membrane,  one  lobe 
lining  each  valve  of  the  shell. 

/?.  The  continuity  of  the  two  lobes  on  the  dorsal 
side  of  the  animal;  their  separation  along 
most  of  its  ventral  side,  where  each  forms  a 
thick  yellowish  free  border. 

7.  The  union  of  the  two  pallial  lobes,  for  a  short 
distance,  towards  the  posterior  part  of  their 
ventral  border. 

8.  The  rudimentary  dot  sal  and  "ventral  siphons, 
separated  from  one  another  at  the  point  of 
union  y  and  each  marked  out  by  a  part  of 
the   mantle-edge  covered  by  short  hair-like 
processes :  the  dorsal  siphon  completely  closed 
below  and  forming  a  narrow  oval  slit;   the 


XL]  THE  FRESH- WATER  MUSSEL.  115 

ventral  siphon  open  below  and  continuous  with 
the  cleft  between  the  ventral  edges  of  the 
mantle-lobes. 
€.      The  branchial  or  pattial  chamber:  turn  back 

the  ventral  edge  of  that  mantle-lobe  from  which 
the  shell  has  been  removed :  a  chamber  is  thus 
exposed  into  which  the  ventral  siphon,  and  the 
cleft  continuous  with  it,  lead. 

£.  The  cloacal  chamber:  pass  a  probe  through  the 
dorsal  siphon;  it  will  enter  a  small  chamber, 
separated  from  the  pallial  chamber  by  a  par- 
tition which  unites  the  hinder  part  of  the  two 
inner  gills  (c.  /?). 

c.      The  contents  of  the  pallial  chamber. 

a.  The  foot:  a  large,  yellowish,  somewhat  plough- 
share-shaped mass,  in  the  middle  line;  its  apex 
directed  forwards  and  ventrally,  towards  the 
front  of  the  cleft  between  the  mantle-lobes. 

(3.  The  gills  or  bronchia :  two  lamellar  bodies 
on  each  side  of  the  foot,  but  reaching  farther 
back  than  it  does :  the  outer  gill  on  each  side, 
attached  to  the  mantle-lobe;  the  inner, attached 
to  the  foot  in  front,  but  farther  back,  separated 
by  a  cleft  from  it;  and  behind  the  foot,  united 
across  the  middle  line  with  its  fellow  so  as  to 
form  a  partition  separating  the  cloacal  from 
the  pallial  chamber. 

y.  The  labial  palps :  a  pair  of  small  triangular 
processes  on  each  side,  in  front  of  the  gills 
and  on  the  dorsal  end  of  the  anterior  edge  of 
the  foot. 

8—2 


1 1 6  ELEMENTAR  Y  BIO  LOG  Y.  [CHAP. 

8.  The  mouth:  each  labial  palp  is  continuous  with 
its  fellow  across  the  middle  line,  and  between 
the  lip-like  ridges  thus  formed,  lies  the  wide 
mouth-opening. 

d.  The  anterior  and  posterior  adductor  muscles:  if 
the  reflected  mantle-lobe  be  turned  down  again, 
-the  oval  divided  ends  of  the  adductor  muscles 
can  be  seen.  They  appear  to  perforate  the 
mantle. 

3.  Now  remove  the  animal  completely  from  its  shell,  by 
detaching  the  other  mantle-lobe  from  the  valve  to 
which  it  is  fixed,  and  cutting  through  the  attachments 
of  the  adductor  muscles  to  that  valve.     The  thick 
dorsal  border  of  the  animal  and  the  continuity  01 
the  mantle-lobes  will  now  be  more  readily  made  out 
than  they  could  be  previously  (2.  b.  ft). 

4.  The  heart. 

a.  On  the  dorsal  border  of  the  animal  is  a  clear 
space,  where  the  mantle  is  very  thin  and  covers- 
in  a  cavity  filled  with  fluid.     This  cavity  is  the 
pericardium,  and  through  its  walls  the  heart  can 
be  seen  beating. 

b.  Pin  the  Anodon  out  in  water  between  two  pieces 
of  loaded  cork,  or  paraffin,  so  that  its  dorsal 
border  is  upwards,  a  mantle-lobe  spread  over 
each  bit  of  cork,  and  its  foot  and  gills  hanging 
down  between  the  two  pieces :  then  carefully  cut 
away  the  dorsal  side  of  the  pericardium  without 
injuring  the  heart. 

c.  The  heart  will  now  be  exposed;  it  is  a  yellow- 
ish transparent  sac,  exhibiting  regular  contrac- 


XI. J  THE  FRESH-WATER  MUSSEL.  117 

tions  and  composed  of  a  median  and  two  lateral 

chambers. 

a.  The  venticle,  or  median  chamber;  an  oval  sac, 
from  each  end  of  which  a  large  vessel  (anterior 
and  posterior  aorta)  is  continued  ;  running 
through  the  middle  of  the  ventricle  is  seen 
part  of  the  alimentary  canal.  All  parts  of 
the  wall  of  the  ventricle  do  not  contract  to- 
gether; but  a  sort  of  wave  of  contraction 
passes,  from  one  end  of  it  to  the  other,  like 
the  peristaltic  contraction  of  the  intestine  in 
one  of  the  higher  animals. 

j3.  The  auricles;  one  of  these  will  be  seen  on  each 
side  if  the  ventricle  be  gently  pushed  out  of 
the  way:  each  is  a  somewhat  pyramidal  sac, 
continuous  with  the  ventricle  at  the  apex  of 
the  pyramid. 

5.     The  organs  of  Bojanus, 

a.  Divide  the  alimentary  canal  at  the  posterior  part 
of  the  pericardiac  chamber  and  turn  it  and  the 
heart  forwards,  so  as  to  lay  bare  the  floor  of  the 
pericardium.     Running  along  the  middle   line 
of  this  floor  will  be  seen  a  large  blood-sinus, 
the  great  vena  cava;  on  each  side  of  this,  the 
floor  is  formed  by  the  roof  of  a  transparent  sac 
(the  non-glandular  part  of  the  organ  of  Bojanus\ 
through  which  is  seen  a  dark  brown  mass  (the 
glandular  fart  of  the  organ  of  Bojanus). 

b.  At  the  extreme  front  end  of  the  pericardiac  floor, 
immediately  under  the  point  at  which  the  in- 
testine enters  the  cavity,  will  be  found  a  pair  of 
oval  openings;  pass  into  each  a  bristle,  tipped 


n8  ELEMENTARY  BIOLOGY.  [CHAP. 

with  a  small  knob  of  sealing-wax  to  prevent  it 
from  perforating  a  passage  for  itself :  the  open- 
ing will  be  found  to  lead  into  a  channel  which 
runs  along  the  glandular  part  of  the  organ  of 
Bojanus. 

c.  Remove  carefully  the  thin  transparent  roof  of  the 
non-glandular  part  of  the  organ  of  Bojanus,  on 
one  side,  so  as  to  lay  bare  the  portion  of  the 
glandular  part  which  lies  within  the  non-glandu- 
lar: the  bristle  will  be  found  to  leave  the  passage 
in  the  glandular  portion  by  an  aperture,  which 
puts  it  in  communication  with  the  non-glandular 
part,  and  is  situated  on  the  upper  side  of  the 
glandular  part,  opposite  the  posterior  end  of  the 
pericardium.     The  glandular  part  extends  back 
some  way  beyond  this  point;  but  it  is  imbedded 
closely  in  the  neighbouring  tissues,  and  is  not 
contained  in  the  loose  non-glandular  sac,  which 
reaches  back  no  farther  than  the  posterior  end 
of  the  pericardium. 

d.  Examine  the  floor  of  the  non-glandular  part,  at 
its  anterior  end :  in  it  will  be  found  a  small 
aperture;  gently  push  a  guarded  bristle  through 
this :  then  turn  the  animal  over,  and  detach  the 
front  end  of  the  inner  gill  on  the  same  side,  from 
the  foot.     The  bristle  will  be  found  to  have 
passed  out  by  an  aperture  (external  opening  of  the 
organ  of  Bojanus)  which  lies  just  above  the  attach- 
ment of  the  gill  to  the  body. 

6.     The  gills  or  branchiae. 

a.      Cut  out  one  of  the  gills  and  examine  it;  it  will  be 
found  to  consist  of  two  lamellae  united  by  their 


xi.]  THE  FRESH-WATER  MUSSEL.  119 

ventral  edges  and  enclosing  a  central  cavity, 
which  opens  into  a  chamber  (epibranchial}  above, 
which  is  continued  back  to  open  into  the  cloacal 
chamber.  The  cavity  between  the  lamellae  is 
subdivided  by  irregular  partitions,  which  pass 
from  one  lamella  to  the  other. 

b.  Carefully  cut  out  a  bit  of  the  wall  of  the  gill-sac 
on  one  side;  mount  in  water  and  examine  with 
i  inch  obj.     The  outer  surface  will  be  seen  to  be 
formed  by  parallel  vertical  bars,  containing  pairs 
of  short  rods;  the  inner  face  being  formed  by  a 
meshwork  of  large  vessels,  perforated  by  wide 
apertures. 

c.  Examine  with  a  higher  power:  the  margins  of 
each  cleft  will  be  found  covered  with  large  active 
cilia. 

7.     The  nervous  system. 

a.     The  cerebral  ganglia. 

a.  These  will  be  found  by  carefully  dissecting 
away  the  bases  of  the  labial  palps  and  the 
integument  on  the  dorsal  side  of  the  mouth. 
They  are  two  in  number,  each  about  the  size 
of  a  pin's  head,  and  somewhat  triangular  in 
form. 

#.  The  commissures  connected  with  the  cerebral 
ganglia  are — 

A  short  cord  uniting  the  two  ganglia  across 
the  middle  line  over  the  mouth. 

A  cord,  the  cerebra-pedal  commissure,  which 
runs  downwards  and  backwards  from  each  and 
becomes  continuous  with  that  which  runs  for- 


ELEMENTARY  BIOLOGY.  [CHAP. 

wards  from  the  pedal  ganglion  of  the  same 
side  (b.  ft). 

A  long  slender  cord  which  passes  directly 
backwards  from  each  beneath  the  organ  of 
Bojanus  and  joins  the  parieto-splanchnic  gan- 
glia of  the  same  side  (c). 

b.  The  pedal  ganglia. 

u.  Lay  the  animal  on  one  side  and  proceed  gently 
to  scrape  away  the  tissues  of  the  foot  at  about 
the  junction  of  its  anterior  with  its  middle 
third,  where  the  muscular  and  the  visceral 
'portions  of  the  foot  join.  The  pedal  ganglia 
will  thus  be  brought  into  view.  They  are  a 
pair  of  deep-orange-coloured  oval  bodies,  each 
rather  larger  than  a  big  pin's  head ;  they  are 
applied  to  one  another  in  the  middle  line. 

ft.  From  each  ganglion  one  commissure!  cord 
(a.  ft)  passes  forwards  and  upwards  to  the 
cerebral  ganglion  of  its  side,  and  branches  are 
given  off  to  the  muscles  of  the  foot  and  to  the 
auditory  organ. 

c.  The  parieto~splanchnic  ganglia. 

a.  This  pair  are  readily  found  by  turning  the 
animal  on  its  dorsal  side,  and  dissecting  away 
the  integument  from  the  ventral  surface  of  the 
posterior  adductor  muscle. 

ft.  Trace  forwards  from  each  the  cord  (a.  ft) 
which  runs  to  the  cerebral  ganglion  of  the 
same  side.  It  is  easy  to  follow  the  commissure 
so  long  as  it  lies  in  the  region  of  the  organ  of 
Bojanus — difficult  further  on. 


XI.]  THE  FRESH-WATER  MUSSEL.  121 

8.  The  auditory  organ. 

a.  This  is  rather  difficult  to  dissect  out  in  Anodon: 
it  is  a  small  sac  which  may  be  found  by  tracing 
back  the  posterior  cord  given  off  from  the  pedal 
ganglion,  to  a  branch  of  which  it  is  attached. 
There  is  usually  an  auditory  vesicle  connected 
with  each  pedal  ganglion. 

b.  If  a  fresh  Cyclas1  be  obtained,  and  its  foot  re- 
moved, mounted  in  water,  and  examined  with 
i  inch  obj.,  the  auditory  sac  can  readily  be  seen 
with  a  constantly-trembling  particle,  the  otolith, 
in  it. 

9.  The  alimentary  canal. 

a.  This  should  be  dissected  out  in  another  Anodon 
which  has  been  well  hardened  in  spirit.  Care- 
fully dissect  away  the  thin  layers  of  muscle  which 
cover  the  left  side  of  the  foot :  as  this  is  done 
the  dark-looking  coil  of  the  intestine  will  come 
into  view:  the  two  coils  lying  parallel  to  one 
another  near  the  posterior  border  of  the  foot 
being  probably  those  first  seen.  Continue  to 
pick  away  the  muscles  and  reproductive  caeca 
until  as  much  as  possible  of  the  course  of  the 
intestine  is  exposed.  Make  a  small  hole  in  it  in 
one  of  the  hindermost  coils,  pass  in  the  end  of 
a  blow-pipe  and  inflate :  then  carefully  lay  open 
the  intestine  throughout  its  whole  length  so  as  to 
expose  its  inner  surface;  working  towards  the 
stomach  on  the  one  hand  and  the  rectum  on  the 
other.  Pass  a  guarded  bristle  into  the  mouth  as 
far  as  it  will  readily  go,  and  then  lay  open  the 
1  Cyclas  cornea — a  small  fresh-water  lamellibranchiate  mollusk. 


ELEMENTARY  BIOLOGY.  [CHAP. 

alimentary  canal  along  it,  with  a  pair  of  scissors. 
Then  push  the  bristle  gently  a  little  farther  on, 
and  follow  it  with  the  scissors,  and  so  on,  until 
the  part  where  the  intestine  has  already  been 
laid  open  is  reached. 

b.  The  alimentary  canal  first  runs  towards  the  dorsal 
side  for  a  short  way  (oesophagus),  lying  on  the 
ventral  side  of  the  anterior  adductor  muscle  :  it 
then  dilates  into  an  irregular  sac  (the  stomach)  • 
behind  the  stomach  it  continues  as  a  long  narrow 
tube,  the  intestine;  this  turns  abruptly  down,  be- 
hind the  stomach,  into  the  foot,  running  at  first 
towards  its  postero-inferior  border;  then  curves 
up  and  forwards  in  the  foot  to  near  its  dorsal 
part ;  then  bends  abruptly  down  and  backwards 
again,  parallel  to  its  previous  course,  towards  the 
ventral  part  of  the  foot,  where  it  makes  another 
turn  and  after  running  forwards  some  way  turns 
upwards  and  runs  to  the  anterior  part  of  the 
pericardium,  where  it  turns  backwards  and  runs 
as  a  straight  tube  (the  rectum),  first  through  the 
ventricle  of  the  heart,  and  then  (passing  on  the 
dorsal  side  of  the  posterior  adductor  muscle) 
along  the  dorsal  side  of  the  cloacal  chamber,  in 
which  it  ends  in  an  opening,  the  anus,  placed  on 
a  prominent  papilla. 

f.  On  the  sides  of  the  stomach  lies  a  brownish 
glandular  mass,  the  liver. 

a.  Tease  out  a  bit  of  the  liver  in  water,  and 
examine  with  •§-  obj.  It  is  composed  of 
branched  csecal  tubes  lined  by  a  layer  of 
brownish  epithelial  cells. 


XL]  THE  FRESH-WATER  MUSSEL.  123 

TO.    Keproductive  organs. 

a.  The  animals  are  dioecious,  but  the  reproduc- 
tive organs  are  similarly  constructed  in  both 
sexes  :  they  vary  much  in  size  with  the  season, 
being  large  in  winter  and  spring,  but  small  at 
other  times. 

b.  Close  to  the  external  opening  of  the  organ  of 
Bojanus  will  be  found  another  small  opening 
on  each  side,  this  is  the  generative  opening. 

c.  From  the  generative  opening  can  be  traced 
back  a  duct,  which  divides  into  many  caecal 
branches  which  lie  in  the  upper  part  of  the 
foot. 

ii.    Muscular  system. 

a.  This  is  most  readily  dissected  out  in  a  spe- 
cimen which  has  been  hardened  in  spirit.  The 
chief  muscles  are : 

a.  The  anterior  and  posterior  addtictor  muscles 
which  pass  directly  from  one  valve  of  the 
shell  to  the  other.  These  have  already  been 
seen. 

/?.  The  posterior  retractor  of  the  foot :  this  can 
readily  be  found,  on  each  side,  running  into 
the  foot  from  its  attachment  to  the  shell  in 
front  of  the  posterior  adductor  muscle. 

y.  The  anterior  retractor  of  the  foot:  this  runs 
from  its  attachment  to  the  shell  behind  the 
anterior  adductor  muscle,  into  the  front  of 
the  foot. 

B.  The  protractor  of  the  foot  arises  from  the 
inner  surface  of  the  shell  behind  the  organ 


ELEMENTARY  BIOLOGY.  [CHAP. 

of  the  anterior  adductor  and  below  that  of 
the  anterior  retractor.  Its  fibres  spread  out  in 
a  fan-like  manner  over  the  upper  part  of  the 
foot,  some  of  them  extending  over  the  sur- 
face of  the  liver. 

e.  The  lesser  retractors.  Several  very  small 
muscles  arising  from  the  shell  just  in  front 
of  the  umbo  and  spreading  over  the  surface 
of  the  liver. 

£  The.  intrinsic  foot-muscles:  forming  the 
greater  part  of  the  ventral  portion  of  that 
organ. 

ry.      Small  muscles  attached  to  each  mantle-lobe, 
at  some  little  distance  from  its  swollen  free 
edge  and  fixed  to  the  shell  along  a  linear 
impression,  which  runs  from  one  adductor  to 
the  other  and  is  termed  ft&pattiallint* 
b.      Tease  out  in  -glycerine  a  bit  of  one  of  the  mus- 
cles which  has  been  treated  with  0-5^  chromic 
acid  solution.     Examine  with  -J  inch  obj.     It 
is  composed  of  spindle-shaped  flattened  cells, 
in  each  of  which  lies  an  elongated  nucleus : 
the  substance  surrounding  the  nucleus  is  clear, 
but  the  rest  of  the  cell  is  granular  and  con- 
tains a  great  number  of  small  particles  arranged 
pretty  definitely  in  transverse  rows.  While  these 
muscular  fibres  agree   in   form  with  those  of 
smooth  muscles,  in  minute  structure  they  ap- 
proach striped  muscles. 

12.    The  shell  or  exoskeleton. 

a.      Its  two  hardened  lateral  pieces  or  valves ;  each 
with  a  straight  dorsal  and  a  curved  ventral  edge, 


XL]  THE  FRESH-WATER  MUSSEL.  125 

and  an  anterior  larger  and  posterior  smaller 
end :  note  the  soft  uncalcified  ventral  edge  of 
each  valve. 

b.  The  limbo;   a  small  blunt   eminence   on   the 
dorsal  border  of  each  valve  near  its  anterior 
end. 

c.  The  ligament:  an  elastic  uncalcified  part  of  the 
exoskeleton  behind  the  umbones,  uniting  the 
two  valves  and  tending  to  keep  their  ventral 
edges  slightly  separated. 

d.  The  markings  on  the  shell. 

a.  External  markings.  The  outside  of  the  shell 
is  greenish  brown,  and  on  it  are  seen  a  num- 
ber of  concentric  lines  generally  parallel  to 
the  margin  of  the  shell,  and  more  numerous 
towards  the  ventral  edge. 

J3.  Internal  markings.  The  interior  of  the  valve 
is  white  and  iridescent :  on  it  are  seen,  near 
the  dorsal  border,  two  oval  marks,  the  ante- 
rior and  posterior  adductor  impressions. 

Joining  the  two  adductor  impressions  is 
a  curved  line,  the  pallial  impression,  which 
marks  where  the  muscles  of  the  edge  of  the 
mantle  were  fixed  to  the  shell. 

In  front  of  the  posterior  adductor  impres- 
sion is  seen  a  small  mark,  indicating  where 
the  posterior  retractor  muscle  was  fixed. 

Behind  the  anterior  adductor  impression 
are  two  marks,  one  opposite  its  upper,  the 
other  opposite  its  lower  end :  the  former 
indicates  the  point  of  attachment  of  the 


1 26  ELEMENTAR Y  BIOLOGY.  [CHAP.  xi. 

anterior  retractor,  the  latter  of  the  protractor 
pedis  muscle. 

Extending  from  each  adductor  impression 
towards  the  umbo  is  a  fainter,  gradually  ta- 
pering impression,  which  may  be  followed 
into  the  cavity  of  the  umbo,  and  indicates 
the  successive  attachments  of  the  adductor 
muscles,  as  the  animal  has  increased  in  size. 

13.  In  the  breeding  season,  examine  the  contents  of  the 
testis  for  spermatozoa,  and  those  of  the  ovary  for 
ova.  Note  the  micropyle  of  the  latter.  If  the  outer 
gill  appear  to  be  thick  and  distended,  it  will  be  found 
full  of  the  larvae  of  the  Anodon, — Glochidium.  Note 
the  characters  of  their  shells  and  the  entangled  fila- 
ments, or  byssus,  with  which  they  are  provided. 


XII. 


THE  FRESH-WATER  CRAYFISH  (Astacus  fiuviatilis) 
AND  THE  LOBSTER  (Homarus  vulgaris). 

THE  Crayfish  and  the  Lobster  are  inhabitants  of  the  water, 
the  former  occurring  in  many  of  our  rivers  and  the  latter 
abounding  on  the  rocky  parts  of  the  coasts  of  the  European 
seas.  They  are  bilaterally  symmetrical  animals,  provided 
with  many  pairs  of  limbs,  among  which  the  large  prehensile 
'claws'  are  conspicuous.  They  are  very  active,  walking 
and  swimming  with  equal  ease  and  spmetimes  propelling 
themselves  backwards  or  forwards,  with  great  swiftness,  by 
strokes  of  the  broad  fin  which  terminates  the  body.  They 
have  conspicuous  eyes,  mounted  upon  moveable  stalks,  at 
the  anterior  end  of  the  head ;  and  two  pairs  of  feelers,  one 
pair  of  which  are  as  long  as  the  body,  while  the  other  pair 
are  much  shorter. 

The  body  and  limbs  are  invested  by  a  strong  jointed 
shell,  or  exoskekton,  which  is  a  product  of  the  subjacent  epi- 
dermis, and  consists  of  layers  of  membrane  which  remain 
soft  and  flexible  in  the  interspaces  between  the  segments  of 
the  body  and  limbs,  but  are  rendered  hard  and  dense  else- 
where by  the  deposit  of  calcareous  salts;  the  exoskeleton 
is  deeply  tinged  with  a  colouring  matter  which  turns  red 
when  exposed  to  the  action  of  boiling  water.  Trie  body 
presents  an  anterior  division — the  cephalothorax — covered 


128  ELEMENTARY  BIOLOGY.  [CHAP. 

by  a  large  continuous  shield,  or  carapace;  and  a  posterior 
division — the  abdomen — divided  into  a  series  of  'segments 
which  are  moveable  upon  one  another  in  the  direction  of 
the  vertical  median  plane,  so  that  the  abdomen  can  be 
straightened  out,  in  extension  ;  or  bent  into  a  sharp  curve,  in 
flexion.  Of  these  segments  there  are  seven.  The  anterior 
six  are  the  somites  of  the  abdomen,  and  each  of  them  has  a 
pair  of  appendages  attached  to  its  ventral  wall.  The  seventh 
bears  no  appendages  and  is  termed  the  telson.  The  anus  is 
situated  on  the  ventral  aspect,  beneath  the  telson  and  behind 
the  last  somite. 

A  groove  on  the  surface  of  the  carapace,  which  is  termed 
the  cervical  suture,  separates  an  anterior  division,  which 
belongs  to  the  head  or  cephalon,  from  a  posterior  division 
which  covers  the  thorax ;  and  the  thoracic  division  of  the 
carapace  further  presents  a  central  region,  which  covers 
the  head,  and  wide  lateral  prolongations,  which  pass  down- 
wards and  cover  the  sides  of  the  thorax,  their  free  ven- 
tral edges  being  applied  against  the  bases  of  the  thoracic 
limbs.  These  are  the  branchiostegites.  Each  roofs  over  a 
wide  chamber  in  which  the  gills  are  contained  and  which 
communicates  with  the  exterior,  below  and  behind,  by  the 
narrow  interval  between  the  edge  of  the  branchiostegite  and 
the  limbs.  Anteriorly  and  inferiorly,  the  branchial  chamber 
is  prolonged  into  a  canal,  which  opens  in  front  and  below 
at  the  junction  of  the  head  with  the  thorax.  \  In  this  canal 
there  lies  a  flat  oval  plate — the  scaphognathite — which  is 
attached  to  the  second  pair  of  maxillae  and  which  plays  a 
very  important  part  in  the  performance  of  the  function  of 
respiration.  Of  the  thoracic  limbs  themselves  there  are 
eight  pairs,  and,  on  the  ventral  face  of  the  body,  the  lines 
of  demarcation  between  the  eight  somites  to  which  these 
limbs  belong  may  be  observed.  There  is  no  trace  of  any 


KIT.]  THE  FRESH-WATER   CRAYFISH.  129 

corresponding  divisions  in  the  cephalothorax  of  the  Lobster; 
but,  in  the  Crayfish,  the  last  thoracic  somite  is  incompletely 
united  with  those  which  precede  it.  The  four  posterior 
pairs  of  thoracic  limbs  are  those  by  which  the  animal  walks 
and  are  termed  the  ambulatory  legs.  The  next  pair  is  formed 
by  the  great  claws  or  chelce.  The  anterior  three  pairs  are 
bent  up  alongside  the  mouth  and  are  moved  to  and  from 
the  median  line  so  as  to  play  the  part  of  jaws,  whence  they 
are  termed  foot-jaws  or  maxillipedes.  The  external  or  third 
pair  of  these  maxillipedes  are  much  stouter  and  more  like 
the  ambulatory  limbs  than  the  rest,  and  the  inner  edges  of 
their  principal  joints  are  toothed.  The  innermost  or  first 
pair  of  maxillipedes  are  broad,  foliaceous  and  soft  When 
these  foot-jaws  are  taken  away,  two  pairs  of  soft  foliaceous 
appendages  come  into  view.  They  are  attached  to  the 
hinder  part  of  the  cephalon  and  are  the  jaws  or  maxillce. 
The  second,  or  outermost,  is  produced,  externally,  into  the 
scaphognathite,  which  will  be  seen  to  lie  in  a  groove  which 
separates  the  head  from  the  thorax  laterally  and  is  the 
cervical  groove. 

Anterior  to  these  maxillae  lie  the  two  very  stout  man- 
dibles. Between  their  inner  toothed  ends  is  the  wide  aper- 
ture of  the  mouth,  bounded,  in  front,  by  a  soft  shield-shaped 
plate,  the  labrum;  and  behind,  by  another  soft  plate,  divided 
by  a  deep  median  fissure  into  two  lobes,  which  is  the  meta- 
stoma.  Thus  far,  the  surfaces  of  the  somites  to  which  the 
appendages  are  attached  look  downwards,  when  the  body  is 
straightened  out  and  the  carapace  is  directed  upwards. 
But,  in  front  of  the  mouth,  the  wall  of  the  body  to  which 
the  appendages  are  attached  is  bent  up,  at  right  angles  to  its 
former  direction,  and  consequently  looks  forwards.  This 
bend  of  the  ventral  wall  of  the  body  is  the  cephalic  flexure. 
In  correspondence  with  this  change  of  position  of  the  sur- 
M.  9 


130  ELEMENTARY  BIOLOGY.  [CHAP. 

face  to  which  they  are  attached,  the  three  pairs  of  append- 
ages of  the  somites  which  lie  in  front  of  the  mouth  are 
directed  either  forwards,  or  forwards  and  upwards.  The 
posterior  pair  consists  of  the  long  feelers  or  antenna:  the 
next,  of  the  short  feelers  or  antennuks;  and  the  most  anterior 
is  formed  by  the  short  subcylindrical  stalks  (pphthalmites\ 
on  the  ends  of  which  the  eyes  are  situated. 

This  enumeration  shews  that  the  Lobster  and  Crayfish 
have  six  pairs  of  abdominal  appendages — the  swimmerets ; 
eight  pairs  of  thoracic  appendages  (four  pairs  of  ambulatory 
limbs,  one  pair  of  chelate  prehensile  limbs,  three  pairs  of 
maxillipeds),  and  six  pairs  of  cephalic  appendages  (two  pairs 
of  maxillae,  one  pair  of  mandibles,  one  pair  of  antennas,  one 
pair  of  antennules,  one  pair  of  eyestalks),  making  in  all  twenty 
pairs  of  appendages.  In  correspondence  with  the  number  of 
appendages  the  body  consists  of  twenty  somites ;  of  which  six 
remain  moveable  upon  one  another  to  form  the  abdomen, 
while  the  other  fourteen  are  united  to  form  the  cephalothorax. 

The  branchiostegite  is  an  outgrowth  of  the  dorsolateral 
region  of  the  confluent  thoracic  somites.  The  serrated 
rostrum  which  ends  the  carapace  is  a  fixed  median  pro- 
longation of  the  dorsal  wall  of  the  anterior  cephalic  somites ; 
while  the  telson  is  a  moveable  median  prolongation  of  the 
dorsal  wall  of  the  sixth  abdominal  somite.  The  labrum  and 
the  metastoma  are  median  growths  of  the  sterna  of  the 
praeoral  and  post -oral  somites. 

Thus  the  whole  skeleton  in  these  animals  may  be  con- 
sidered as  a  twentyfold  repetition  of  the  ring-like  somite 
with  its  pair  of  appendages,  which  is  seen  in  its  simplest 
form  in  one  of  the  abdominal  somites.  Moreover,  not- 
withstanding the  great  variety  of  functions  allotted  to  the 
various  appendages,  the  study  of  the  details  of  their  struc- 
ture (see  Laboratory  work)  will  shew  that  they  are  all  re- 


xri.]  THE  FRESH-WATER   CRAYFISH.  131 

ducible  to  modifications  of  a  fundamental  form,  consisting 
of  a  basal  joint  (protopodite)  with  three  terminal  divisions 
(endopodite,  exopodite,  epipodite). 

As  has  been  already  said,  the  Lobster  and  Crayfish  are 
bilaterally  symmetrical ;  that  is  to  say,  a  median  vertical 
plane  passing  through  the  mouth  and  anus  divides  them  into 
two  similar  halves.  •  This  symmetry  is  exhibited  not  merely 
by  the  exterior  of  the  body  and  the  correspondence  of  the 
paired  limbs,  but  extends  to  the  internal  organs ;  the  alimen- 
tary canal  and  its  appendages,  the  heart,  the  nervous  sys- 
tem, the  muscles  and  the  reproductive  organs,  being  dis- 
posed so  as  to  be  symmetrical  in  relation  to  the  median 
vertical  plane  of  the  body. 

The  wide  gullet  leads  almost  vertically  into  the  spacious 
stomach,  and  both  are  lined  by  a  chitinous  continuation  of 
the  exoskeleton.  The  stomach  is  divided  by  a  transverse 
constriction  into  a  spacious  cardiac,  and  a  much  smaller 
pyloric  division,  from  which  latter  the  intestine  passes.  The 
walls  of  the  anterior  half  of  the  cardiac  sac  are  thin  and 
membranous,  but,  in  the  posterior  half,  they  become  calci- 
fied so  as  to  give  rise  to  a  gastric  skeleton  of  considerable 
complexity.  The  chief  part  of  this  skeleton  consists  of  a 
median  dorsal  T-shaped  ' cardiac'  ossicle,  the  cross-piece 
of  which  forms  a  transverse  arch,  while  its  long  median 
process  extends  backwards  in  the  middle  line.  The  ends  of 
the  transverse  arch  are  articulated  obliquely  with  two  small 
*  antero-lateral '  pieces,  the  extremities  of  which  again  are 
articulated  with  postero-lateral  pieces,  and  these  unite  with 
a  cross-piece,  the  '  pyloric '  ossicle,  which  arches  over  the 
roof  of  the  pyloric  division  of  the  stomach.  In  this  manner 
a  sort  of  hexagonal  frame  with  moveable  joints  is  formed, 
and  the  median  process  projects  backwards  so  far,  as  to  end 

9—2 


j32  ELEMENTARY  BIOLOGY.  [CHAP. 

below  the  pyloric  piece.  It  is  connected  with  this,  however, 
by  a  short  '  pre-pylbric '  ossicle  which  ascends  obliquely 
forwards  and  is  articulated  with  the  anterior  edge  of  the 
pyloric  piece.  The  lower  extremity  of  this  is  produced  into 
the  strong  median  'uro-cardiac'  tooth;  two  small  'cardiac' 
teeth  are  borne  by  the  median  process  of  the  cardiac  ossicle; 
while  the  postero-lateral  pieces  are  flanged  inwards,  and, 
becoming  greatly  thickened  and  ridged,  form  the  large 
'  lateral  cardiac '  teeth.  Two  powerful  muscles  are  attached 
to  the  cardiac  ossicle,  and  ascend  obliquely  forwards 
to  be  inserted  into  the  under  face  of  the  carapace. 
Two  other  similar  muscular  bundles  arise  from  the  pyloric 
ossicle,  and,  passing  obliquely  upwards  and  backwards,  are 
also  inserted  into  the  under  face  of  the  carapace.  The  dis- 
position of  all  these  parts  is  such  that  when  these  muscles 
contract,  the  uro-cardiac  tooth  moves  forwards  and  down- 
wards, while  the  lateral  teeth  move  inwards  downwards  and 
backwards,  and  the  three  meet  in  the  middle  line.  )frhe 
action  of  these  muscles  can  be  readily  imitated  by  seizing 
the  anterior  and  posterior  cross-pieces  with  forceps  and 
pulling  them  in  the  direction  in  which  the  muscles  act.  The 
three  teeth  will  then  be  seen  to  come  together  with  a  clash. 
Thus  the  food  which  has  been  torn  by  the  jaws  is  submitted 
to  further  crushing  in  this  gastric  mill.  The  walls  of  the 
pyloric  division  of  the  stomach  are  thick,  and  project  like 
cushions  into  its  interior,  thereby  reducing  its  cavity  to  a 
narrow  passage.  The  cushion-like  surfaces  of  the  pyloric 
walls  are  provided  with  long  hairs  which  stretch  across  this 
narrow  passage,  and  thus  convert  it  into  a  strainer,  which 
allows  of  the  passage  of  only  very  finely  divided  matter  from 
the  gastric  sac  to  the  thin  and  delicate  intestine.  The 
hepatic  ducts  open,  one  on  each  side,  at  the  junction  of  the 
pyloric  division  of  the  stomach  with  the  intestine.  The 


xii.]  THE  FRESH-WATER   CRAYFISH.  133 

intestine  is  slender  and  delicate,  smooth  internally  in  the 
Lobster,  papillose  in  the  Crayfish.  Near  its  hinder  end  its 
walls  become  thicker  for  a  short  distance,  and  this  thick- 
ened portion,  with  which,  in  the  Lobster,  a  short  dorsal 
cascum  is  connected,  may  be  regarded  as  the  large  intestine 
or  rectum. 

The  heart  is  a  short,  thick,  somewhat  hexagonal,  symmetri- 
cal organ  lodged  in  the  pericardiac  sinus,  to  the  walls  of  which 
it"  is  attached  by  fibrous  bands.  In  its  anterior  half  three 
pairs  of  apertures  are  visible,  two  being  placed  upon  the 
upper  face,  two  at  the  sides,  and  two  on  the  under  face.  The 
lateral  apertures  are  the  most  posterior,  the  dorsal,  the  most 
anterior  in  position.  Each  aperture  begins  in  a  funnel- 
shaped  depression  of  the  outer  face  of  the  organ,  which  leads 
obliquely  inwards  and  terminates  by  a  valvular  slit  in  the 
cavity  of  the  heart.  This  cavity  is  very  much  reduced  by 
the  encroachment  of  the  muscular  bands  which  constitute 
the  walls  of  the  heart,  so  that  a  transverse  or  longitudinal 
section  shews  only  a  small  median  cavity  surrounded  by  a 
thick  and  spongy  wall. 

During  life,  the  heart  beats  vigorously,  the  whole  of  its 
parietes  contracting  together.  From  the  dorsal  part  of  its 
anterior  extremity  three  arteries  are  given  off,  one  median 
and  two  lateral,  to  the  cephalon  and  its  contents,  and  from 
the  ventral  aspect  of  this  end  of  the  heart  an  hepatic  artery 
is  given  off,  on  each  side,  to  the  liver.  At  its  posterior  end, 
the  heart  ends  in  a  median  dilatation  from  which  two  great 
arterial  trunks  are  given  off ;  one  the  superior  abdominal 
artery,  which  runs  along  the  dorsal  face  of  the  intestine, 
giving  off  transverse  branches  as  it  goes,  in  each  somite ;  and 
the  other,  the  sternal  artery,  which  passes  ventrally  to  the 
interspace  between  the  penultimate  and  antepenultimate 


134  ELEMENTARY  BIOLOGY.  [CHAP. 

thoracic  ganglia,  passes  between  their  commissures  and 
divides  into  two  branches,  which  run,  backwards  and  for- 
wards, between  the  ganglionic  chain  and  the  exoskeleton. 

These  arteries  divide  and  subdivide  and  end  in  what,  in 
some  parts  of  the  body  at  any  rate,  e.g.  the  liver,  is  a  true 
capillary  system.  The  veins  are  irregular  channels,  or 
sinuses,  which  lie  between  the  several  muscles  and  viscera. 
One  of  the  largest  of  these  is  situated  in  the  median  ventral 
line,  and  can  be  readily  laid  open  by  piercing  the  soft  inte- 
gument which  lies  between  any  two  of  the  abdominal  sterna. 
The  blood  flows  out  of  the  aperture  with  great  rapidity,  and 
the  quantity  shed  shews  the  size  of  the  sinus  and  its  free 
communication  with  the  rest  of  the  vascular  system.  By 
cutting  across  any  one  of  the  limbs  and  inserting  a  blow- 
pipe into  the  place  whence  the  blood  wells  forth,  this  ventral 
sinus  can  be  readily  injected  with  air.  A  large  and  irregular 
sinus  is  also  to  be  found  in  the  median  dorsal  region  of  the 
abdomen  and  is  freely  connected  with  the  median  ventral 
sinus.  The  stem  of  each  branchia  contains  two  canals,  one 
running  along  its  outer  and  the  other  along  its  inner  face. 
The  outer  canal  communicates,  at  its  origin,  with  the  median 
ventral  sinus.  The  inner  canal  opens  into  a  passage  which 
ascends  in  the  lateral  wall  of  the  thorax  and  opens,  after 
meeting  with  other  l  branchio-cardiac>  canals,  opposite  the 
lateral  aperture  of  the  heart.  As  the  valvular  lips  of  this 
and  the  other  apertures  of  the  heart  open  inwards,  the  blood, 
when  the  systole  takes  place,  is  driven  out  of  the  heart 
through  the  various  arteries,  and  a  considerable  part  of  the 
blood  thus  propelled  into  the  capillaries  is  collected  by  the 
median  ventral  sinus  and  thence,  passing  through  the  gills, 
eventually  returns  to  the  heart,  which  is  therefore,  like  the 
heart  of  Anodon,  a  systemic  and  not  a  branchial  heart.  But 
whether  the  whole  of  the  venous  blood  takes  the  same 


xii.]  THE  FRESH-WATER   CRAYFISH.  135 

course,  or  whether  some  of  it  returns  from  the  dorsal  sinuses 
directly  to  the  pericardium,  is  a  question  which  is  not  de- 
cided. Nor  is  it  certain  whether  the  so-called  pericardium 
is  to  be  regarded  as  one  cavity,  or  whether  the  fibrous  bands, 
which  connect  the  heart  with  its  walls,  may  not  subdivide  it 
into  compartments  in  immediate  communication  with  cer- 
tain of  the  cardiac  apertures,  and  not  with  the  rest. 

In  the  Lobster,  from  which  the  blood  is  readily  obtained 
in  quantity,  it  is  a  nearly  colourless  fluid,  which  usually  has 
a  faint  neutral  tint.  It  readily  coagulates,  a  tolerably  firm 
clot  separating  from  the  serum.  It  contains  nucleated  cor- 
puscles, devoid  of  any  noticeable  colour,  which  throw  out 
very  long  pseudopodial  prolongations,  and  thereby  take  an 
irregularly  stellate  form. 

It  has  been  seen  that  the  respiratory  organs,  or  branchiae, 
are  lodged  in  a  chamber  situated  between  the  branchiostegite 
externally,  the  lateral  walls  of  the  thoracic  somites  internally, 
and  the  bases  of  the  thoracic  limbs  below;  and  that  there 
is  a  narrow  interspace  between  the  free  edge  of  the  bran- 
chiostegite and  the  latter.  At  the  anterior  end  of  the  cham- 
ber, a  funnel-shaped  passage  leads  to  the  anterior  opening 
mentioned  above,  and,  in  this  passage,  the  scaphognathite 
lies  like  a  swing  door. 

During  life,  the  scaphognathite  is  in  incessant  movement 
forwards  and  backwards,  scooping  out  the  water  in  the  bran- 
chial chamber  through  its  anterior  aperture  at  every  forward 
motion.  The  place  of  the  water  thus  thrown  out  is  taken  by 
water  which  flows  in  by  the  inferior  and  posterior  cleft  be- 
neath the  free  edge  of  the  branchiostegite,  and  thus  a  constant 
current  over  the  gills  is  secured.  Each  branchia  is  somewhat 
like  a  bottle-brush,  having  a  stem  beset  with  numerous  fila- 
ments; and  the  blood  contained  in  the  vessels  of  the  latter 


i36  ELEMENTARY  BIOLOGY.  [CHAP. 

being  separated  by  only  a  very  thin  membrane  from  the  air 
contained  in  the  water,  loses  carbonic  anhydride  and  gains  a 
corresponding  amount  of  oxygen  in  its  course  through  the 
branchiae. 

The  branchiae  are  attached  partly  to  the  epimera  of  the 
thoracic  somites,  partly  to  the  proximal  ends  of  the  thoracic 
limbs.  The  epipodites  of  the  limbs  ascend  between  the  sets 
of  branchiae  which  belong  to  each  somite,  and  separate  them. 
The  branchiae  which  are  attached  to  the  limbs  must  neces- 
sarily be  stirred  by  the  movement  of  the  latter,  and  hence  the 
exchange  of  gases  between  the  blood  which  they  contain,  and 
the  water  must  be,  to  a  certain  extent,  increased,  in  propor- 
tion to  the  muscular  contractions  which  give  rise  to  the 
movements  of  the  limbs  and  the  consequently  increased 
formation  of  carbonic  anhydride. 

The  mode  and  place  of  the  excretion  of  nitrogenous 
waste  is  not  yet  clearly  made  out,  but  it  seems  probable 
that  two  large  green  glands  which  lie  in  the  cephalon,  close 
to  the  bases  of  the  antennae,  are  renal  organs.  Each  gland 
encircles  the  neck  of  a  large  thin-walled  sac  which  opens  by 
a  short  canal  upon  the  ventral  face  of  the  basal  joint  of  the 
antenna. 

The  nervous  system  consists  of  a  chain  of  thirteen  gan- 
glia— united  by  longitudinal  commissures — lodged  in  the 
median  line  of  the  ventral  aspect  of  the  body,  from  which 
nerves  are  given  to  the  organs  of  sense,  to  the  muscles 
of  the  trunk  and  limbs,  and  to  the  integuments;  and  of  a 
visceral  nervous  system,  developed  chiefly  upon  the  stomach. 

Of  the  thirteen  ganglia,  the  most  anterior  lies  in  the 
cephalon,  close  to  the  attachments  of  the  three  anterior  pair 
of  appendages,  and  gives  branches  to  them  and  to  the  vis- 
ceral nervous  system.  It  is  usually  termed  the  brain  or  the 
siipraozsophageal  ganglion.  It  is  connected  by  two  commis- 


xii.]  THE  FRESH-WATER   CRAYFISH.  137 

sural  cords,  which  pass  on  each  side  of  the  gullet,  with 
a  larger  ganglionic  mass,  which  is  called  the  subozsophageal 
ganglion.  This  occupies  the  region  of  the  hinder  part  of 
the  cephalon  and  the  anterior  part  of  the  thorax,  and  gives 
off  nerves  to  the  maxillae  and  the  three  pair  of  maxillipeds. 
Five  other  ganglia  lie  in  the  five  somites  which  bear  the 
chelae  and  the  ambulatory  limbs,  and  there  is  one  for  each 
abdominal  somite,  the  last  of  these  being  the  largest  of  the 
six. 

The  longitudinal  commissures  between  the  abdominal 
ganglia  are  single ;  but,  in  the  thorax,  the  commissures  are 
double,  and  the  ganglia  themselves  shew  more  or  less  evi- 
dent indications  of  being  double.  And  there  is  reason  to 
believe  that  these  thirteen  apparent  ganglia  really  represent 
twenty  pairs  of  primitive  ganglia,  one  pair  for  each  somite ; 
the  three  pairs  of  praeoral  ganglia  having  coalesced  into  the 
brain ;  and  the  five  which  follow  the  mouth  having  united 
into  the  suboesophageal  mass. 

The  only  organs  of  special  sense  which  are  recognizable 
in  the  Lobster  and  Crayfish  are  eyes  and  auditory  organs. 

The  eyes  are  situated  at  the  extremities  of  the  eyestalks, 
or  ophthalmites,  which  represent  the  first  pair  of  appendages 
of  the  head.  The  rounded  end  of  the  eyes  talk  presents  a 
clear,  smooth  area  of  somewhat  crescentic  form,  divided  into 
a  great  number  of  small  four-sided  facets.  This  area  cor- 
responds with  the  cornea,  which  is  simply  the  ordinary 
chitinous  layer  of  the  integument  become  transparent. 
The  inner  face  of  each  facet  of  the  cornea  corresponds  with 
the  outer  end  of  an  elongated  transparent  slightly  conical 
body — the  crystalline  cone — the  inner  end  of  which  passes  into 
a  relatively  long  and  slender  connective  rod,  by  which  it  is 
united  with  a  spindle-shaped  transversely  striated  body — 


1 38  ELEMENTAR Y  BIOLOGY.  [CHAP. 

the  striated  spindle.  The  inner  extremity  of  this  again  is 
connected  with  the  convex  surface  of  the  dilated  cushion- 
shaped  ganglionic  termination  of  the  optic  nerve.  The 
respective  striated  spindles,  connective  rods  and  crystalline 
cones,  thus  radiate  from  the  outer  surface  of  the  terminal 
ganglion  to  the  inner  surface  of  the  cornea,  and  each  is 
separated  from  its  neighbour  by  a  nucleated  sheath,  parts  of 
which  are  deeply  pigmented.  Nothing  is  accurately  known 
as  to  the  manner  in  which  the  function  of  vision  is  per- 
formed by  the  so-called  compound  eye  which  has  just  been 
described.  The  inner  and  outer  faces  of  the  corneal  facets 
are  flat  and  parallel.  They  therefore  cannot  play  the  part 
of  lenses ;  and,  if  they  could,  there  is  no  trace  of  nerve 
endings  so  disposed  as  to  be  affected  by  the  points  of  light 
gathered  together  in  the  foci  of  such  lenses.  Morphologi- 
cally, the  cones,  connective  rods  and  striated  spindles,  are 
in  many  ways  analogous  to  those  elements  of  the  retina  of 
the  Vertebrata  which  make  up  the  layers  of  rods  and  cones 
and  the  granular  layers.  These  structures  are  properly 
modifications  of  the  epidermis;  inasmuch  as  the  cerebral 
vesicle,  of  which  the  retinal  vesicles  are  outgrowths,  are  in- 
volutions of  the  epidermis  of  the  embryo,  and,  morphologi- 
cally speaking,  the  free  ends  of  the  rods  and  cones  of  the 
vertebrate  eye  are,  as  in  the  crustacean,  turned  outwards. 
It  seems  probable,  therefore,  that  the  crustacean  eye  is  to  be 
compared  to  the  retina  alone  of  the  vertebrate  eye,  and  that 
vision  is  performed  as  it  would  be  by  the  retina  deprived  of 
its  refractive  adjuncts. 

The  auditory  organ  of  the  Lobster  and  Crayfish  is  situated 
in  the  basal  joint  of  the  antennule,  on  the  dorsal  surface  of 
which/a  small  slitjjke  opening,  protected  by  numerous 
is  to  be  seen/yThe  chitinous  layer  of  the  integument 
is  invaginated  at  this  opening,  and  thus  gives  rise  to  a  small 


xn.j  THE  FRESH-WATER  CRAYFISPL  139 

flattened  sac  lodged  in  the  interior  of  the  antennule.  One 
side  of  this  sac  is  in-folded  so  as  to  produce  a  ridge,  which 
projects  into  the  cavity  of  the  sac,  and  is  beset  with  very 
fine  and  delicate  hairs.  The  auditory  nerve  enters  the  fold, 
and  its  ultimate  filaments  reach  the  bases  of  these  hairs. 
The  sac  contains  water  in  which  minute  particles  of  sand 
are  suspended. 

The  sexes  are  distinct  in  the  Lobster  and  Crayfish.  The 
external  characters  of  the  males  and  females  and  the  form 
of  the  reproductive  organs  are  described  in  the  Laboratory 
work. 

The  impregnated  ova  are  attached  in  great  numbers,  by 
a  viscid  secretion  of  the  oviduct,  to  the  hairs  of  the  swim- 
merets,  where  they  undergo  their  development.  A  Lobster 
with  eggs  thus  attached,  is  said  by  the  fishermen  to  be 
'  in  berry.'  In  the  Crayfish,  the  embryo  passes  through  all 
the  stages  which  are  needed  to  bring  it  very  near  to  the 
form  of  the  adult  before  it  leaves  the  egg:  but,  in  the 
Lobster,  the  young,  when  hatched,  are  larvae  extremely  un- 
like the  parent,  which  undergo  a  series  of  metamorphoses  in 
order  to  attain  their  adult  condition.  The  larvae  may  fre- 
quently be  obtained  by  opening  the  eggs  of  a  *  hen-lobster ' 
in  '  berry.'  They  have  a  rounded  carapace,  two  large  eyes, 
a  jointed  abdomen  devoid  of  appendages ;  and  the  thoracic 
limbs  are  provided  with  long  exopodites. 

The  ordinary  growth,  no  less  than  the  metamorphoses 
of  the  Lobster  and  Crayfish,  are  accompanied  by  periodical 
castings  of  the  outer,  chitinous,  layer  of  the  integument. 
After  each  such  ecdysis,  the  body  is  soft  and  the  animal 
retires  into  shelter  until  the  '  shell '  is  reproduced. 


i4o  ELEMENTARY  BIOLOGY.  [CHAP. 

LABORATORY  WORK. 

i.     General  external  characters. 

The  animal  is  covered  by  a  dense  exoskeleton:  in  it 
are  readily  recognised  the  following  parts  : — 

a.     The  body  proper  : 

a.  Its  anterior  unsegmented  portion  (cephalotho- 
rax) :  the  great  shield-like  plate  (carapace) 
covering  the  back  and  sides  of  the  cephalotho- 
rax ;  the  groove  across  the  carapace  (cervical 
suture)  marking  out  the  line  of  junction  of 
head  proper  and  thorax:  the  anterior  pro- 
longation of  the  carapace  to  form  the  frontal 
spine. 

ft.  The  posterior  segmented  portion  (abdomen)-. 
its  seven  divisions ;  the  anterior  six  much  like 
one  another;  the  most  posterior  (telsoii) 
different  from  the  rest. 

/;.  The  great  number  of  jointed  limbs  (appendages] 
attached  to  the  ventral  aspect  of  the  body :  their 
varying  characters  in  different  regions. 

c.      The  external  apertures  of  the  body. 

a.  The  mouth;  seen  by  separating  the  append- 
ages beneath  the  head. 

(3.  The  anus;  a  longitudinal  slit  beneath  the 
telson. 

y.  The  paired  genital  openings:  in  the  male,  on 
the  first  joints  of  the  last  pair  of  appendages 
of  the  thorax:  in  the  female,  on  the  first  joints 
of  the  last  thoracic  appendages  but  two. 


xn.]  THE  FRESH-WATER   CRAYFISH.  i4i 

[d.     The  openings  of  the  auditory  organs. 
e.     The  openings  of  the  green  glands. 

These  will  be  more  readily  found  when  the  ap- 
pendages on  which  they  are  situated  have  been 
separated.  See  21.  f  and  g.~\ 

-2.      Examine  carefully  the  third  abdominal  segment  or 
scmite  and  its  appendages. 

a.      The  segment  proper:   arched  above;  flattened 

below. 

a.  Its  dorsal  part  (tergttm),  with  an  anterior 
smooth  portion  overlapped  by  the  preceding 
segment  in  extension  of  the  abdomen,  and  a 
posterior  rougher  part  overlapping  part  of  the 
succeeding  segment. 

/?.  The  ventral  surface  of  the  segment :  united 
with  the  corresponding  portions  of  the  preced- 
ing and  succeeding  segments  by  a  flexible 
membrane. 

y  The  point  of  union  of  the  appendages  with 
the  somite. 

£.  The  sternum:  that  portion  of  the  ventral  sur- 
face of  the  somite,,  which  lies  between  the 
points  of  attachment  of  the  appendages. 

c.      The  epimeron:  the  portion  of  the  ventral  sur- 
face which  lies  on  each  side  external  to  the. 
attachment  of  the  appendage. 
This  region  is  very  short  and  passes  almost  - 
directly  into  the  inner  walls  of  the  pleuron. 

£.  The  downward  extension  (J>leurori)  of  the 
lateral  walls  of  the  somite  formed  by  the  pro- 
longation of  the  tergum  and  epimeron:  the 


142  ELEMENTARY  BIOLOGY.  [CHAP. 

smooth  facet  on  the  anterior  half  of  the 
pleuron  where  it  is  overlapped  by  the  one  in 
front. 

I.      The  appendages  or  swimmerets:  one  on  each  side: 
the  structure  of  each — 

a.  The  short  two-jointed  basal  portion  (protopo- 
dite), consisting  of  a  shorter  proximal  and  a 
longer  distal  piece. 

/?.  The  antero-posteriorly  flattened  elongated 
lamellae  attached  to  the  distal  joint  of  the 
protopodite,  an  inner  (endopodite)  and  outer 
(exopodite). 

3.  The  fourth  and  fifth  abdominal  segments :    closely 
resembling  the  third. 

4.  The  sixth  abdominal  segment:  its  modified  append- 
ages. 

a.  The  protopodite :  represented  by  a  single  short 
strong  joint.  (In  the  lobster  there  is  an  in- 
complete basal  joint.) 

J3.  The  exopodite  and  endopodite  :  wide  plates 
fringed  with  setse  :  the  exopodite  divided  into 
two  portions  by  a  transverse  joint. 

5.  The  telson. 

A  flattened  plate  bearing  no  appendages  :  sub- 
divided by  a  transverse  joint  (it  is  undivided  in 
the  lobster) :  the  membranous  character  of  the  greater 
part  of  the  ventral  surface  of  its  anterior  division. 

The  tail-fin ;  formed  by  the  telson  and  the  append- 
ages of  the  sixth  abdominal  segment. 


xii.]  THE  FRESH-WATER   CRAYFISPL  143 

6.  The  second  abdominal  segment. 

Closely  resembling  the  third  in  the  female  :  in  the 
male  its  appendages  are  modified :  the  protopodite 
and  basal  joint  of  endopodite  much  elongated,  and 
the  latter  produced  into  a  plate  rolled  upon  itself  so 
as  to  form  a  demicanal,  concave  inwards.  (In  the 
lobster  the  endopodite  is  produced  inwardly,  into  an 
oval  process.) 

7.  The  first  abdominal  segment :  its  appendages ;   rudi- 
mentary in  the  female  (it  has  only  one  instead  of 
two  terminal  divisions  in  the  lobster) :  in  the  male 
consisting  of  a  single  plate  rolled  in  upon  itself.    (In 
the  lobster  the  single  terminal  division  has  the  form 
of  a  flat  scoop  or  a  narrow  spoon  with  its  concave 
side  turned  inwards.) 

8.  The  structure  of  the  cephalothorax. 

a.  Note  again  the  carapace,  with  its  frontal  spine 
and  cervical  suture. 

/3.  Turn  the  animal  over  and  note  the  very 
narrow  sterna  between  the  points  of  attach- 
ment of  the  thoracic  appendages. 

The  last  thoracic  somite  is  not  completely 
ankylosed  with  the  one  in  front,  on  the  verti- 
cal side  in  the  crayfish.  In  the  lobster  it  is. 

y.  Raise  with  a  pair  of  forceps  the  free  edge  of 
the  lateral  part  of  the  carapace  which  lies  just 
over  the  bases  of  the  thoracic  appendages,  and 
is  termed  the  branchiostegite :  note  that  it  is 
formed  by  the  large  united  pleura  of  the 
thoracic  segments,  and  overlaps  a  chamber  in 
which  the  gills  lie. 


4  ELEMENTARY  BIOLOGY.  [CHAP. 

9.  Note  the  plane  in  which  the  sterna  of  the  anterior 
three  somites  of  the  animal  (marked  out  by  their 
appendages)  lie — it  is  nearly  at  right  angles  to  the 
plane  of  the  remaining  sterna  of  the  cephalothorax — 
so  that  their  appendages  are  directed  forwards  in- 
stead of  downwards. 

10.  Cut  a  vertical  section  of  a  piece  of  the  exoskeleton 
which  has  been  decalcified  by  lying  in  i£  chromic 
acid  solution  for  a  few  days. 

a.  It  will  be  seen  to  be  composed  of  a  large  number 
of  parallel  laminae  which  are  thicker  towards 
the  outer  part.      The  laminae  are  marked  by  ill- 
defined  parallel  lines  which  run  perpendicular  to 
the  surface,  and  which  give  their  edges  a  striated 
appearance.    The  outermost  layer  is  more  trans- 
parent than  the  rest  and  wants  this  striation. 

b.  The  epidermis  lying  beneath  the  innermost  of  the 
above  laminae  is  composed  of  ill-defined  branched 
nucleated  granular  cells :  the  outermost  giving  off 
a  large  number  of  short  processes  which  end  in 
clubbed  ends  and  penetrate  a  short  way  into  the 
exoskeleton. 

11.  The  respiratory  organs.    Remove  now  the  branchio- 
stegite  on  one  side  and  examine  the  gills:  they  are 
1 8  in  number,  arranged  in  two  sets. 

a.  Six  are  attached  to  the  epipodites  of  some  of 
the  appendages  (2nd  and  $rd  maxillipedes, 
chelae,  ist,  2nd,  and  3rd  pair  of  ambulatory 
limbs). 

/?.  The  remaining  12  are  fixed  to  the  sides  of 
the  body,  and  each  consists  of  a  central  stem 
giving  off  a  number  of  delicate  filaments. 


xii.]  THE  FRESH-WATER   CRAYFISH.  145 

y.  Cut  away  the  gills,  noting  the  two  large  chan- 
nels in  the  stem  of  each,  and  observe  the 
cervical  groove  at  the  front  of  the  gill-chamber 
with  the  scaphognathite  (21.  d.  a.)  lying  in  it. 

[8.  In  the  lobster  there  are  20  gills  on  each  side, 
arranged  as  in  the  crayfish,  except  that  there  are 
14  on  the  side  of  the  body.] 

12.  Circulatory  organs.  Immerse  the  animal  in  water 
with  its  ventral  surface  downwards :  cut  away  care- 
fully with  a  pair  of  scissors  the  dorsal  part  of  the 
carapace  which  lies  behind  the  cervical  suture  and 
that  part  of  the  wall  of  the  thorax  from  which  the 
gills  have  been  removed. 

A  chamber  (the  pericardial  sinus)  is  thus  laid  bare 
in  which  lies  a  polygonal  sac,  the  heart* 

a.  The  six  openings  from  the  sinus  into  the  heart  ; 
two  superior,  two  inferior,  and  two  lateral :  pass 
bristles  into  them.     The  arteries  arising  from  the 
heart;  five  anterior,  one  (ophthalmic)  single  in 
the  middle  line,  the  others  (antennary  and  hepatic) 
in  pairs;  one,  the  sternal,  the  largest  of  all,  given 
off  from  the  posterior  end. 

b.  Cut  away  the  terga  of  the  abdominal  somites  and 
follow  back  the  superior  abdominal  branch  of  the 
sternal  artery,  removing  carefully  the  muscles 
which  lie  over  it  in  the  abdominal  region.     It 
will  be  seen  as  a  transparent  tube  lying  in  the 
middle  line  on  the  intestine  (14.  £.),  or  in  the 
female  lobster  separated  from  it  anteriorly  by 
the  posterior  ends  of  the  two  ovaries.     It  gives 
off  branches  from  its  upper  side  to  the  muscles 
over  it,  and  also  a  pair  of  branches  which  run  out 

M.  10 


i .,6  ELEMENTARY  BIOLOGY.  [CHAP. 

laterally  in  the  intervals  between  each  pair  of 
somites.  In  the  sixth  abdominal  somite  it  termi- 
nates by  splitting  up  into  three  or  four  large 
branches  which  pass  in  a  radiating  manner  into 
the  telson.  On  account  of  the  small  size  of  the 
crayfish  this  artery  is  difficult  to  dissect  in  it. 

c.  The  sternal  artery  presents  an  enlargement  at  its 
commencement  just  where  the  above  branch 
arises  from  it.  It  then  passes  vertically  down- 
wards towards  the  ventral  surface,  passing  on 
one  side  of  the  intestine.  Its  subsequent  course 
must  be  followed  later  (15). 

13.   Reproductive  organs. 

These  differ  considerably  in  the  crayfish  and  the  lob- 
ster. They  lie  partly  beneath  the  heart,  which  must 
therefore  be  removed  or  pushed  on  one  side  in  order 
to  see  them.  Both  animals  are  unisexual. 

a.      Of  the  Crayfish. 

a.  The  testis.  A  trilobed  yellowish  mass :  two  of 
its  lobes  are  larger  than  the  third  and  pass 
forwards  side  by  side  in  the  middle  line :  the 
third  lobe  is  directed  backwards. 

/?.  The  two  vasa  deferentia  arise  just  where  the 
posterior  lobe  of  the  testis  meets  the  two  ante- 
rior. Each  is  narrow  near  the  gland,  but 
widens  as  it  proceeds  back  from  it,  and  be- 
coming extremely  convoluted,  finally  ends  at 
the  genital  opening  on  its  own  side  (i.  c.  y.). 
Trace  the  course  of  the  vas  deferens  on  that 
side  from  which  the  thoracic  wall  has  been 
removed  (12). 


xii.]  THE  FRESH-WATER   CRAYFISH.  147 

y.  Tease  out  a  bit  of  the  testis  in  water,  and  ex- 
amine with  \  obj. :  it  will  be  seen  to  be  com- 
posed of  sacculated  tubes.  In  it  or  in  the 
vas  deferens  some  of  the  spermatozoa  may  be 
found :  they  are  motionless  and  have  the  form 
of  nucleated  cells  provided  with  radiating  pro- 
cesses. 

B.  The  ovary  is  a  gland  in  shape  and  colour 
very  similar  to  the  testis  of  the  male.  From 
it  two  short  oviducts  arise  and  pass  almost 
directly  downwards  to  the  genital  openings 

(I.  *  y.). 

b.      Of  the  Lobster. 

a.  The  testes  are  two  long  tubes  which  lie  partly 
in  the  thorax  and  partly  in  the  abdomen. 
Their  posterior  portions  meet  in  the  middle 
line,  but  in  front  they  diverge,  and  about  one 
fourth  the  length  of  each  from  its  anterior  end 
a  short  transverse  branch  unites  the  two. 

/?.  The  vas  deferens  arises  a  little  in  front  of  the 
middle  of  each  testis  and  passes  without  con- 
volutions towards  the  genital  opening.  Its 
distal  half  is  dilated. 

v.  Tease  out  a  bit  of  the  testis  in  water  and  ex- 
amine with  -|  obj.  for  spermatozoa.  They  are 
motionless,  and  consist  of  an  elongated  cell 
from  one  end  of  which  three  rigid  pointed 
processes  radiate. 

8.  The  ovaries  of  the  lobster  are  also  elongated 
and  lie  partly  in  the  thorax  and  partly  in  the 
abdomen,  above  the  alimentary  canal  (14). 

IO— -2 


148  ELEMENTARY  BIOLOGY.  [CHAP. 

Each  is  a  dark  green  mass,  on  the  exterior  of 
which  minute  rounded  eminences  (indications 
of  the  contained  ova)  can  be  seen.  Near 
their  anterior  ends  they  lie  in  contact  in  the 
middle  line,  and  for  a  short  distance  their 
substance  is  continuous. 

e.  An  oviduct  arises  from  each  ovary  a  little  in 
front  of  its  middle,  and  passes  directly  to  the 
genital  opening  of  its  own  side  (i.  c.  y.). 

14.  Alimentary  organs. 

a.  Remove  the  dorsal  part  of  the  carapace  in  front 
of  the  cervical  suture,  and  there  will  then  be 
laid  bare,  in  front  of  the  position  of  the  heart, 
a  large  sac — the  stomach ;  pass  a  probe  into  it 
along  the   gullet,    through    the   mouth-opening 
which  lies  between  the  mandibles. 

b.  Trace  back  the  tubular  intestine  from  the  stomach 
to  the  anus.     It  dilates  near  the  latter  in  the 
lobster.     In  the  crayfish  it  presents  a  small  coecal 
diverticulum  close  to  the  stomach,  and  in  the 
lobster  one  near  the  anus. 

c.  Examine  the  liver. 

a.  It  is  an  elongated  soft  pale-yellow  mass  lying 
in  each  side  of  the  cephalo-thorax,  and  opening 
by  a  duct  on  each  side  at  the  point  where  the 
intestine  joins  the  stomach. 

p.  Tease  out  a  bit  of  the  liver  in  water;  it  is 
made  up  of  branched  ccecal  tubes,  which  when 
examined  microscopically  are  seen  to  be  lined 
by  a  layer  of  cells  (epithelium). 


xii.]  THE  FRESH-WATER   CRAYFISH.  149 

d.      Carefully  remove  the  alimentary  canal,  cutting 
the  gullet  through  close  to  the  stomach. 

a.  Open  the  latter  under  water  and  make  out  in 
it  the  constriction  which  divides  it  into  an 
anterior  (cardiac)  and  a  posterior  (pyloric) 
portion. 

/?.  The  supporting  bars  and  the  hairs  in  the 
stomach,  and  the  calcifications  of  its  lining 
membrane. 

15.  Now  trace   the   sternal    artery   (removing   the   ali- 
mentary canal  and  the  genital  organs),  until  it  enters 
a  passage  (sternal  canal)  formed  by  ingrowths  of  the 
exoskeleton  near  the  ventral  surface  of  the  animal. 
Just   before   entering  this  the  sternal  artery  gives 
off  the  inferior  abdominal  branch,  which  runs  back 
along  the  middle  line  of  the  abdomen  immediately 
inside  the  sterna  of  the  somites.     Trace  this  branch 
back  removing  the  muscles  which  cover  it.     By  this 
proceeding  the  abdominal  part  of  the  nervous  chain 
will  be  exposed.    It  lies  immediately  above  the  blood- 
vessel and  is  not  to  be  injured.  , 

1 6.  The  nervous  system. 

a.  Find  the  sitpraozsophageal  ganglion  in  front  of 
the  gullet. 

/?.  The  circumozsophageal  commissures  passing 
back  from  it. 

y.  Follow  back  these  commissures,  cutting  away 
the  hard  parts  (forming  the  roof  of  the  sternal 
canal)  which  come  in  the  way;  they  lead  to 
a  chain  of  six  ganglia,  lying  along  the  floor  of 
the  cephalothorax,  and  united  by  double  cords 


i5o  ELEMENTARY  BIOLOGY.  [CHAP. 

(commissures).  Lying  in  the  sternal  canal  be- 
neath the  ganglia  may  be  seen  the  sternal 
artery  (15). 

8.  Follow  back  the  single  cord  proceeding  from 
the  last  thoracic  ganglion  to  the  abdomen, 
removing  any  muscles  which  come  in  the  way : 
it  will  lead  to  a  chain  of  six  ganglia,  one  for 
each  abdominal  segment,  united  by  single 
cords. 

17.  The  green  gland.     A  soft  greenish  mass  lying  on 
each  side  in  the  extreme  front  part  of  the  cephalo- 
thoracic  cavity:   pass  a  fine  bristle  into  it  from  the 
opening  of  its  duct  on  the  basal  joint  of  the  endo- 
podite  of  the  antenna  (2i./). 

1 8.  Tease   out  a  bit  of  muscle  in  water  and  examine 
it  microscopically:  note  its  structure;  it  is  made  up 
of  fibres,  marked  by  regularly  alternating  transverse 
lighter  and  darker  bands. 

19.  Tease  out  a  bit  of  perfectly  fresh  nerve-cord  in  water 
and  stain  with  magenta  or  hsematoxylin. 

a.  Composed  of  slender  fibres  of  varying  size,  each 
consisting  of  a  structureless  outer  wall,  on  which 
are  nuclei  at  intervals,  surrounding  a  clear  or, 
sometimes,  finely  granular  or  obscurely  fibrillated 
central  axis. 

20.  Tease  out  in  water  a  ganglion  which  has  been  treated 
with  osmic  acid. 

a.  Composed  of  large  oval  branched  cells,  each  con- 
sisting of  a  granular  mass  in  which  lies  a  clear 
round  nucleus,  containing  a  nucleolus. 


xii.]  THE  FRESH-WATER    CRAYPISH.  151 

21.  The  appendages.  Beginning  with  the  sixth  abdomi- 
nal segment,  remove  with  forceps  the  appendages  of 
the  body  and  arrange  them  in  order  on  a  piece  of 
cardboard.  The  abdominal  appendages  have  been 
already  described;  note  the  following  points  in  the 
remainder,  working  from  behind  forwards. 

a.     The  four  posterior  thoracic  appendages  (ambii- 
latory  appendages}. 

a.  The  most  posterior:  elongated  and  seven- 
jointed,  the  joints  working  in  different  planes 
so  that  the  limb  as  a  whole  can  move  in  any 
direction :  the  joints  have  the  following  names; 
the  proximal,  short  and  thick,  coxopodite;  the 
next,  small  and  conical,  basipodite;  next,  cylin- 
drical and  marked  by  an  annular  constriction, 
ischiopodite ;  the  next,  longer,  meropodite;  then 
successively,  the  carpopodile,  propodite,  and 
dadylopodite.  Probably  the  coxo-  and  basi- 
podite together  represent  the  protopodite  of 
the  abdominal  appendages  :  the  remaining 
joints  the  endopodite:  the  exo-  and  epipodite 
are  wanting. 

/?.  The  next  ambulatory  leg:  generally  similar 
to  the  preceding,  but  possessing,  attached  to 
the  coxopodite,  a  long  membranous  flattened 
appendage  (epipodite}  which  ascends  into  the 
gill-chamber:  it  bears  a  gill. 

y.  The  next  anterior  ambulatory  leg:  differing 
from  the  last  only  in  having  its  propodite 
prolonged  so  as  to  be  opposable  to  the  dac- 
tylopodite  and  form  a  pair  of  forceps 


ELEMENTARY  BIOLOGY.  [CHAP. 

8.  The  most  anterior  ambulatory  leg :  resembling 
y.  closely  and,  like  it,  bearing  a  gill. 

b.  The  great  cheltz:  much  larger  and  more  powerful 
than  the  last  appendage:  but  resembling  it  in 
structure,  except  that  its  ischio-podite  and  basi- 
podite  are  ankylosed  together;  it  carries  a  gill. 

c.  The  three  maxillipedes. 

a.  The  most  posterior :  its  short  thick  basal  two- 
jointed  (protopodite) :  the  three  prolongations 
articulated  to  it;  the  external  (epipodite}  a 
curved  elongated  lamina  lying  in  the  branchial 
chamber  and  bearing  a  gill ;  the  middle  one 
(exopodite)  long,  slender  and  many-jointed; 
the  internal  one  (endopodite)  several-jointed 
and  much  resembling  one  of  the  ambulatory 
limbs. 

/?.  The  middle  maxillipede :  much  like  a.  but 
with  the  two  joints  of  the  protopodite  fused 
together  and  with  a  less  stout  endopodite. 

7.  The  anterior  maxillipede;  protopodite,  exopo- 
dite  and  epipodite  all  present,  but  smaller 
than  those  of  {3.  and  the  epipodite  bearing  no 
gill ;  the  endopodite  flattened  and  foliaceous. 
The  ambulatory  limbs,  great  chelae,  and 
maxillipedes  together  constitute  the  append- 
ages of  the  thorax ;  we  now  come  to  those  of 
the  head  proper. 

d.  The  two  maxilla. 

a.  The  posterior:  its  protopodite  and  endopodite 
essentially  like  those  of  the  anterior  maxilli- 
pede; the  epipodite  and  exopodite  united  and 


xn.]  THE  FRESH-WATER   CRAYFISH.  153 

forming  a  wide  oval  plate  (scaphognathite) 
which  lies  at  the  anterior  end  of  the  gill- 
chamber  (n.  y.). 

/?.      Anterior  maxilla :    epipodite  and  exopodite 
undeveloped  :  the  endopodite  foliaceous. 

e.  The  mandible.     Its  strong  toothed  basal  joint 
(protopodite)  bearing  a  small  appendage  (the palp] 
which  represents  the  endopodite ;  the  epipodite 
and  exopodite  unrepresented. 

f.  The  antenna.  Its  two-jointed  basal  portion  (proto- 
podite) bearing  a  flattened  plate  (the  rudimentary 
exopodite)  and  a  long  multiarticulate  filament  (the 
endopodite]'.  the  opening  of  the  green  gland  (17) 
on  the  oral  side  of  the  basal  joint  of  the  proto- 
podite. 

g.  The  antennula.     Its   large  trigonal  basal  joint 
(protopodite),  bearing  a  pair  of  jointed  filaments 
(endopodite  and  exopodite):   the  opening  of  the 
auditory  organ  (24)  in  the  midst  of  a  minute 
hairy  tuft  on  the  basal  joint. 

h.      The  ophthalmites  or  eyestalks.     Short  two-jointed 
appendages  representing  only  the  basipodite. 

22.  Now  work  back  over  the  20  pairs  of  appendages 
and  compare  each  with  the  third  maxillipede :   all 
may  be  supposed  to  be  derived  from  it  by  suppression, 
coalescence  or  special  change  of  form;  it  is  what  is 
called  a  typical  appendage. 

23.  Structure  of  the  Eye. 

a.     Take  the  eye  of  a  lobster  which  has  lain  four  or 
five  days  in  0-5  per  cent,  solution  of  chromic  acid 


154  ELEMENTARY  BIOLOGY.  [CHAP. 

and  then  twenty-four  hours  or  more  in  alcohol. 
Examine  its  surface  with  one  inch  obj.  with  re- 
flected light.  It  will  be  seen  to  be  marked  out 
into  a  great  number  of  minute  square  areas 
or  facets,  each  of  which  shews  faint  signs  of 
furrows  crossing  it  diagonally  from  corner  to 
corner. 

b.  Imbed  the  eye  and  cut  a  number  of  sections  from 
it  perpendicular  to  its  surface :  mount  in  glycerine 
and  examine  with  one  inch  objective. 

a.  If  the  section  has  passed  through  the  middle 
of  the  eye  it  will  be  seen  to  present  a  central 
mass  (optic  ganglion)  from  which  a  number  of 
lines  appear  to  radiate  to  the  facets  on  the 
surface.  These  radiating  lines  (which  are 
obscured  here  and  there  by  concentric  pig- 
mented  layers)  are  indications  of  the  striated 
spindles,  connective  rods  and  crystalline  cones. 

c.  Examine  your  thinnest  section  with  a  high  power, 
or  tease  out  one  of  your  thicker  ones  in  gly- 
cerine.   Beginning  at  the  exterior  make  out  suc- 
cessively— 

a.  The  cornea,  answering  to  one  of  the  superficial 
facets.  Its  flat  outer  and  slightly  convex  inner 
surface.  Immediately  beneath  the  cornea 
there  will  be  seen  (in  good  specimens)  a 
slightly  granular  layer. 

ft.  The  crystalline  cone,  an  angular  transparent 
body  which  is  usually  obscured  by  pigment. 
If  this  is  the  case,  another  section  must  be 
mounted  in  dilute  caustic  potash,  which  re- 
moves the  pigment. 


xii.  THE  FRESH-WATER  CRAYFISH.  155 

y.  Behind  the  crystalline  cone  comes  the  con- 
nective rod.  It  is  widest  in  front  where  it 
joins  the  cone,  but  narrows  posteriorly  where 
it  is  continuous  with  the  striated  spindle.  If 
fresh  eyes  be  treated  with  osmic  acid  and 
then  teased  out,  each  of  these  rods  can  be 
split  up  into  four  fibres. 

8.  The  striated  body  is  fusiform  and  presents 
well-marked  transverse  striations.  Besides 
these  coarse  striations,  however,  much  finer 
ones  can  be  seen  by  careful  examination  with 
a  high  power.  The  outer  ends  of  these 
spindles  correspond  in  position  to  the  second 
of  the  pigmented  layers  seen  with  the  low 
power  (b.  a.) :  they  are  best  seen  in  specimens 
treated  with  dilute  caustic  potash. 

e.  Beneath  the  striated  spindles  is  a  perforated 
membrane  through  which  the  spindles  pass  to 
become  continuous  with  the  optic  ganglion. 
From  their  ends  pass  nerve-fibres  which  run 
inwards  in  a  converging  manner  and  among 
which  nerve-cells  are  here  and  there  scattered. 
Within  the  ganglion  are  several  concentric 
pigmented  bands. 

£.  If  the  section  has  passed  back  along  the  optic 
nerve  two  obliquely  placed  lenticular  masses 

will  be  seen  among  its  fibres. 

i 
t].      Passing  back  from  the  cornea  to  the   optic 

ganglion  is  a  membrane  investing  each  cone, 
rod,  and  spindle.  It  is  on  this  that  most  of 
the  pigment  lies  which  causes  the  two  outer 
dark  bands.  Over  the  rods  the  pigment  is 


ELEMENTARY  BIOLOGY.  [CHAP. 

wanting  and  there  the  membrane  is  seen  to 

possess  oval  nuclei. 
24.   The  Auditory  organ. 

This  lies  in  the  basal  joint  of  the  antennule  and  is 
best  examined  in  the  lobster.  The  upper  surface  of 
this  basal  joint  is  flat  posteriorly  and  joins  in  front 
at  an  angle  a  rounded  anterior  portion.  It  bears 
several  tufts  of  hairs :  one  of  these  is  very  small  and 
lies  at  the  inner  side  of  the  flattened  surface,  just  at 
the  angle  where  it  meets  the  rounded  part ;  among 
these  hairs  is  the  opening  into  the  auditory  sac, 
through  which  a  bristle  can  easily  be  passed. 

a.  Take  a  fresh  antennule  from  a  lobster  and  cut 
away  the  under  surface  of  its  basal  joint.     A 
chitinous  transparent  sac  will  readily  be  found  in 
it,  among  the  muscles  &c. ;  this  is  the  auditory 
sac  and  is  about  \  of  an  inch  long.     Carefully 
dissect  it  out. 

b.  If  this  sac  be  held  up  to  the  light  a  little  patch 
of  gritty  matter  will  be  seen  on  its  under  surface 
near  the  aperture  to  the  exterior.     Behind  this 
can  be  seen  a  curved  opaque  line ;  behind  this, 
and  concentric  wit}i  it,  a  shorter  brownish  streak. 
Cut   out   carefully  the  part  of  the   sac  which 
bears  these  streaks :  mount  in  sea-water  or  sodic 
chloride  solution  and  examine  with  one  inch  ob- 
jective. 

a.  The  white  line  will  be  seen  to  answer  to  a 
ridge  on  the  apex  of  which  is  a  row  of  large 
hairs,  and  both  on  the  brown  patch  and  on  the 
opposite  side  of  the  main  row  will  be  seen 
scattered  groups  of  smaller  hairs. 


xir.}  THE  FRESH-WATER   CRAYFISH.  157 

c.      Examine  with  -|  obj. 

a.  Each  of  the  hairs  seen  with  the  lower  power  is 
now  seen  to  be  covered  over  its  whole  surface 
with  innumerable  very  fine  secondary  hairs ; 
these  are  shortest  near  the  base  of  the  primary 
hair.  Towards  its  base  each  of  the  primary 
hairs  is  constricted  and  then  dilates  into  a 
bulbous  enlargement  which  is  fixed  to  the 
wall  of  the  sac. 

P.  The  brown  patch  is  seen  to  owe  its  colour  to 
a  single  layer  of  polygonal  epithelial  cells 
containing  pigment  granules. 

y.  By  focussing  through  this  epithelial  layer  a 
number  of  parallel  slightly  granular  bands  is 
seen  passing  up,  one  to  the  base  of  each  hair 
in  the  main  row  on  the  top  of  the  ridge.  At 
the  base  of  the  hair  to  which  it  runs,  each 
band  is  constricted  and,  entering  the  bulbous 
enlargement  of  the  hair,  joins  a  small  hemi- 
spherical swelling  within  it. 

S.  If  a  fresh  auditory  sac  be  put  in  i  per  cent, 
solution  of  osmic  acid  for  half  an  hour,  and 
then  laid  for  twenty-four  hours  in  distilled 
water  and  examined,  each  of  the  granular 
bands  mentioned  above  is  seen  to  consist  of 
a  bundle  of  fine  fibres  which  swell  out  into 
fusiform  enlargements  at  intervals. 

e.  A  great  part  of  the  whole  interior  of  the  audi- 
tory sac  of  the  lobster  is  covered  with  very 
fine  hairs  which  can  only  be  seen  with  a  high 
power.  Epithelium  is  absent  except  the  pig- 
mented  patch  above  mentioned. 


158  ELEMENTARY  BIOLOGY.  [CHAP.  xn. 

d.  The  auditory  sac  in  the  crayfish  is  very  similar  to 
that  in  the  lobster,  and  may  be  examined  in  a 
similar  way.  It  is  however  not  so  good,  both 
on  account  of  its  smaller  size  and  because  the 
auditory  hairs,  although  longer,  are  collected  in 
a  close  tuft,  which  makes  it  more  difficult  to  see 
the  manner  of  their  insertion. 


XIII. 
THE  FROG  (Rana  temporaries  and  Rana  esculentd). 

THE  only  species  of  Frog  indigenous  in  Britain  is  that  .termed 
the  ' common'  or  *  Grass  Frog'  (Rana  temporaria\  while,  on 
the  Continent,  there  is,  in  addition  to  this,  another  no  less 
abundant  species,  the  hind-limbs  of  which  are  considered  a 
delicacy,  whence  it  has  received  the  name  of  the  'Edible 
Frog'  (Rana  esculenta).  Unless  the  contrary  be  expressly 
stated,  the  description  here  given  applies  to  both  species. 
The  Edible  Frog  is  usually  larger  than  the  other,  and  is 
therefore  more  convenient  for  most  anatomical  and  physio- 
logical purposes. 

In  the  body  of  the  Frog  the  head  and  trunk  are  readily 
distinguishable;  but  there  is  no  tail  and  no  neck,  the  con- 
tours of  the  head  passing  gradually  into  those  of  the  body, 
and  the  fore-limbs  being  situated  immediately  behind  the 
head.  There  are  two  pairs  of  limbs,  one  anterior  and  one 
posterior.  The  whole  body  is  invested  by  a  smooth  moist 
integument,  on  which  neither  hairs,  scales,  nor  other  forms  of 
exoskeleton  are  visible;  but  hard  parts,  which  constitute  the 
endoskeldon,  may  readily  be  felt  through  the  integument  in 
the  head,  trunk  and  limbs. 

The  yellowish  ground-colour  of  the  skin  is  diversified  by 
patches  of  a  more  or  less  intense  black,  brown,  greenish,  or 
reddish-yellow  colour,  and,  in  the  Grass  Frog,  there  is  a 
large,  deep  brown  or  black  patch  on  each  side  of  the  head, 


160  ELEMENTARY  BIOLOGY.  [CHAP. 

behind  the  eyes,  which  is  very  characteristic  of  the  species. 
The  coloration  of  different  frogs  of  the  same  species  differs 
widely;  and  the  same  frog  will  be  found  to  change  its  colour, 
becoming  dark  in  a  dark  place,  and  light  if  exposed  to  the 
light. 

The  body  of  the  Frog  presents  only  two  median  aper- 
tures, the  wide  mouth  and  the  small  cloacal  aperture.  The 
latter  is  situated  at  the  posterior  end  of  the  body,  but  rather 
on  its  upper  side  than  at  its  actual  termination.  It  is  com- 
monly termed  the  anus,  but  it  must  be  recollected  that  it 
does  not  exactly  correspond  with  the  aperture  so  termed  in 
the  Mammalia. 

The  two  nostrils,  or  external  nares,  are  seen  at  some  dis- 
tance from  one  another  upon  the  dorsal  aspect  of  the  head, 
between  the  eyes  and  its  anterior  contour.  The  eyes  are 
large  and  projecting,  with  well-developed  lids,  which  shut 
over  them  when  they  are  retracted;  and,  behind  the  eye, 
on  each  side  of  the  head,  there  is  a  broad  circular  area  of 
integument,  somewhat  different  in  colour  and  texture  from 
that  which  surrounds  it;  this  is  the  outer  layer  of  the  mem- 
brane of  the  tympanum,  or  drum  of  the  ear. 

The  fore-legs  are  very  much  shorter  than  the  hind-legs. 
Each  fore-limb  is  divided  into  a  brachium,  antebrachium  and 
manus,  which  correspond  with  the  arm,  fore-arm  and  hand  in 
Man.  The  manus  possesses  four  visible  digits  which  answer 
to  the  second,  third,  fourth,  and  fifth  fingers  in  Man.  There 
is  no  web  between  the  digits  of  the  manus. 

The  hind-legs  are  similarly  marked  out  into  three  divi- 
sions, femur,  crus,  and  £es,  of  which  the  femur  answers  to 
the  thigh,  the  crus  to  the  leg,  and  the  pes  to  the  foot,  in 
Man.  The  pes  is  remarkable  not  only  for  its  great  relative 
size  as  a  whole,  but  for  the  elongation  of  the  region  which 
answers  to  the  tarsus  in  Man.  It  will  be  observed,  however, 


XIIL]  THE  FROG.  161 

that  there  is  no  projecting  heel.  There  are  five  long  and 
slender  digits,  which  correspond  with  the  five  toes  in  Man, 
and  are  united  together  by  thin  extensions  of  the  integu- 
ment constituting  the  web.  The  innermost  and  shortest 
answers  to  the  hattux,  or  great  toe,  in  Man. 

At  the  base  of  the  hallux,  the  integument  of  the  sole 
presents  a  small  horny  prominence,  and  sometimes  there  is 
a  similar  but  smaller  elevation  on  the  outer  side  of  the  foot: 
but  there  are  no  nails  upon  the  ends  of  any  of  the  digits  of 
either  the  pes  or  the  manus.  Thickenings,  or  callosities,  of 
the  integument,  however,  occur  beneath  the  joints  of  the 
digits,  both  in  the  pes  and  the  manus. 

During  the  breeding  season,  the  integument  on  the 
palmar  surface  of  the  innermost  digit  of  the  manus,  in  the 
male,  becomes  converted  into  a  rough  and  swollen  cushion, 
which,  in  the  Grass  Frog,  acquires  a  dark-brown  or  black 
colour. 

The  Frog,  when  at  rest,  habitually  assumes  a  sitting  pos- 
ture much  like  that  of  a  dog  or  cat.  Under  these  circum- 
stances the  back  appears  humped,  the  posterior  half  being 
inclined  at  a  sharp  angle  with  the  anterior  half.  The  ver- 
tebral column,  however,  will  be  found  to  be  straight,  and  the 
apparent  hump-back  arises,  not  from  any  bend  in  the  verte- 
bral column,  but  from  the  manner  in  which  the  long  iliac 
bones  are  set  on  to  the  sacrum. 

The  walk  of  the  Frog  is  slow  and  awkward,  but  it  leaps 
with  great  force,  by  the  sudden  extension  of  the  hind-limbs, 
and  it  is  an  admirable  swimmer. 

In  a  living  Frog,  the  nostrils  will  be  seen  to  be  alter- 
nately opened  and  shut,  while  the  integument  covering  the 
under  side  of  the  throat  is  swollen  out  and  flattened.  The 
alternate  pumping  in  and  expulsion  of  the  air  needed  for  the 
Frog's  respiration  is  connected  with  these  movements. 

M.  II 


162  ELEMENTARY  BIOLOGY.  [CHAP. 

The  upper  eyelid  of  the  Frog  is  large  and  covered  with 
ordinary  pigmented  integument,  and  it  has  very  little  mobility. 
What  performs  the  function  of  the  lower  eyelid  in  Man, 
is  a  fold  of  the  integument  of  -which  very  little  is  pigmented 
and  which  is,  for  the  most  part,  semi-transparent,  so  as  to 
resemble  the  nictitating  membrane,  of  a  bird  rather  than  an 
ordinary  lower  lid.  If  the  surface  of  the  cornea  be  touched, 
the  eyeball  is  drawn  inwards  under  the  upper  lid,  which 
descends  a  little,  at  the  same  toe  as  the  lower  lid  ascends 
over  the  ball>.to  meet  the  upper  lid  and  close  the  eye. 

As  is  well  known,  Frogs  emit  a  peculiar  croaking  sound, 
their  vocal  powers  being  more  -especially  manifested  in  the 
breeding  season,  when  they  collect  together  at  the  surface  ot 
ponds,  pools  and  sluggish  streams,  in  great  numbers.  At 
this  season,  which  commences  in  the  early  spring  for  the 
Grass  Frog,  but  much  later  on  in  the  year,  for,  the  Edible 
Frog,  the  male  seeks  the  female  and,  clasping  her  body 
tightly  with  his  fore-limbs,  remains  in  this  position  for  days 
or  even  weeks,  until  her  ova,  are  discharged,  when  he  fecun- 
dates them  by  a  simultaneous  out-pouring  of  the  seminal 
fluid.  Shortly,  after  the  eggs:  pa^s.  intq  the  water,  the  thin 
layer  of  viscid  albumen,  secreted  by  the  oviduct,  with  which 
each  egg  is  surrounded,  swells,  up  by  imbibition  and,  with 
that  which  .surrounds  the  others,  it  gives  rise,  to  a  gelatinous 
mass  in  which  the  eggs  remain  imbedded  during  the  early 
stages  of  their  development,. 

The  development  of  the  eggs  is  closely  dependent  upon 
temperature,  being  greatly  accelerated  by  warmth  and  re- 
tarded by  cold.  The  process  of  yelk-division,  which  com- 
mences within  a  few  hours  of  impregnation,  is  readily  ob- 
served when  the  eggs  are  examined  as  opaque  objects  under 
a  low  power  of  the  microscope. 

While  still  within  the  egg  the  embryo  assumes  the  form 


Xiii.]  THE  FROG.  163 

of  a  minute  fish,  devoid  of  limbs  and  with  only  rudiments  of 
gills,  but  provided  with  two  adhesive  discs  on  the  ventral 
side  of  the  head  behind  the  mouth. 

After  leaving  the  egg,  the  young  acquires  three  pairs  of 
external  branchitz  having  the  form  of  branched  filaments,  at- 
tached to  the  sides  of  the  hinder  part  of  the  head.  Narrow 
clefts  in  the  skin  at  the  roots  of  the  branchias  lead  into  the 
back  of  the  throat.  Water  taken  in  at  the  mouth  passes  out 
by  these  branchial  clefts.  The  animal  crops  the  aquatic 
plants  on  which  it  lives,  by  means  of  the  horny  plates  with 
which  its  jaws  are  provided. 

In  the  Tadpole,  as  the  larval  Frog  is  called,  the  intestine, 
which  is  relatively  longer  than  in  the  adult,  is  coiled  up  like 
a  watch-spring  in  (the  abdominal  cavity.  A  membranous  lip, 
the  surface  of  which  is  'beset  with  numerous  horny  papillae, 
surrounds  the  mouthy  and  the  muscular  tail  acquires  a  large 
relative  size.  The  eyesj  the  nasal  and  auditory  organs 
become  distinct,  but  no  limbs  are  at  first  visible.: 

A  fold  of  the-,  integument  in  the  hyoidean  region,  called 
the  opercular  membrane,  now  grows  back  over  the  external 
gills  and  unites^with  the.  integument  covering  the  abdomen, 
leaving  only  a  small  aperture  on  the  left  side,  through  which 
the  ends  of  the. .external  gills  of  that  .side. may,  for.  some  time, 
be  seen  to  protrude.  The  external  gills  atrophy  and  are 
succeeded  functionally  by  short  processes  developed  from 
the  opposing  faees  of  the  branchial .  clefts — the  internal 
branchia.  The  rudiments  of  the  limbs  appear,  rapidly  elon- 
gate and  take  on  their  characteristic  shape,  the  hind  pair 
only  being  at  first  visible  on  account  of  the  anterior  pair 
being  hidden  under  the  opercular  membrane.  The  lungs 
are  developed  and,  for  a  time,  the  tadpole  breathes  both  by 
them  and  by  its  internal  gills. 

As  the  legs  grow  the  tail  shortens  and,  at  last,  is  re- 

II 2 


1 64  ELEMENTARY  BIOLOGY.  [CHAP. 

presented  merely  by  the  pointed  end  of  the  body;  the  gape 
elongates  until  the  angle  of  the  mouth  lies  behind  the  eye, 
instead  of  a  long  way  in  front  of  it,  as  in  the  tadpole;  the 
labial  membrane  and  the  horny  armature  of  the  mouth 
disappear,  while  teeth  are  developed  in  the  upper  jaw  and 
on  the  vomers ;  the  intestine  becomes  less  and  less  coiled  as, 
not  growing  at  the  same  rate  as  the  body,  it  becomes  rela- 
tively shorter;  and  the  animal  gradually  changes  its  diet 
from  vegetable  to  animal  matters — the  perfect  Frog  being 
insectivorous. 

The  two  species,  Rana  temporaries  and  Rana  escuknta, 
are  distinguishable  by  the  following  external  characters.  In 
Rana  temporaria,  the  interspace  between  the  eyes  is  flat  or 
slightly  convex,  and  its  breadth  is  usually  greater  than,  or 
at  least  equal  to,  that  of  one  of  the  upper  eyelids.  The 
diameter  of  the  tympanic  membrane  is  less  than  that  of  the 
eye,  often  much  less.  The  horny  elevation  on  the  outer  side 
of  the  pes  is  small  or  absent,  and  that  on  the  inner  is 
flattened  and  has  a  rounded  margin.  A  patch  of  dark 
colour  extends  from  the  eye  backwards  over  the  tympanic 
membrane.  The  males  have  the  cushion  on  the  radial  side 
of  the  manus  black,  and  they  are  devoid  of  vocal  sacs. 

In  Rana  esculenta,  on  the  other  hand,  the  interspace  be- 
tween the  eyes  is  usually  concave  and  narrower  than  the 
breadth  of  one  of  the  eyelids.  The  diameter  of  the  tym- 
panic membrane  is  as  great  as  that  of  the  eye.  The  horny 
elevation  on  the  inner  side  of  the  pes  is  elongated,  com- 
pressed and  brought  to  a  blunt  edge,  so  as  almost  to  resem- 
ble a  spur,  and  a  small  outer  elevation  is  constantly  present. 
There  is  no  patch  of  colour  at  the  sides  of  the  head,  such 
as  exists  in  Rana  temporaria,  and  the  cushion  of  the  inner 
digit  in  the  male  is  not  black.  The  males  have  a  large 
pouch  on  each  side  of  the  head,  behind  the  angle  of  the 


xiii.]  THE  FROG.  165 

jaw,  communicating  with  the  cavity  of  the  mouth,  and,  when 
they  croak,  these  pouches  becoming  dilated  assume  the 
form  of  spherical  sacs. 

Having  thus  become  acquainted  with  the  general  cha- 
racter and  life-history  of  the  Frog,  and  with  those  features 
of  its  organization  which  are  visible  to  the  naked  eye  and 
without  dissection,  its  structure  may  next  be  studied  in. 
detail. 

If  the  abdomen  be  laid  open,  it  will  be  found  to  enclose 
a  cavity  in  which  some  of  the  most  important  viscera — the 
stomach  and  intestine,  the  liver,  the  pancreas,  the  spleen, 
the  lungs,  the  kidneys  and  urinary  bladder,  and  the  repro- 
ductive organs — are  contained.  As  this  cavity  answers  to 
those  of  the  pleurae  and  of  the  peritoneum  in  the  higher 
animals,  it  is  termed  the  pleuroperitoneal  cavity  ;  and  the  soft 
smooth  membrane  which  lines  it  and  covers  the  contained 
viscera  is  the  pleuroperitoneal  membrane. 

The  vertebral  column  traverses  the  middle  of  the  roof  of 
this  cavity,  and  the  layer  of  pleuroperitoneal  membrane 
which  lines  each  lateral  wall  of  the  cavity,  passes  downwards 
on  each  side  of  the  vertebral  column  and  joins  its  fellow  in 
the  middle  line  to  form  a  thin  sheet,  the  mesentery,  which 
suspends  the  intestine.  In  the  triangular  interval  left  between 
these  two  layers  before  they  unite,  a  wide  canal — the  sub- 
vertebral  lymph  sinus — the  dorsal  aorta,  and  the  chain  of 
sympathetic  ganglia,  are  situated. 

The  dorsal  moiety  of  the  anterior  end  of  the  pleuroperi- 
toneal cavity  is  occupied  by  the  gullet,  which  places  the 
mouth  in  communication  with  the  stomach.  Beneath  the 
gullet  the  peritoneal  cavity  is  separated  only  by  a  thin  parti- 
tion from  a  chamber,  the  pericardium,  which  contains  the 
heart.  The  posterior  face  of  the  partition  is  constituted  by 


it>6  ELEMENTARY  BIOLOGY.  [CHAP. 

the  peritoneum,  its  anterior  face  by  a  membrane  of  similar 
character,  the  pericardial  membrane,  which  lines  the  peri- 
cardium and  is  reflected  on  to  the  heart,  in  the  same  way  as 
the  peritoneum  lines  the  peritoneal  cavity  and  is  reflected  on 
to  the  intestine. 

A  layer  of  the  muscular  fibres  which  enter  into  the  walls 
of  the  abdomen  is  continued  inwards  at  the  anterior  boundary 
of  the  pleuroperitoneal  cavity  and  is  attached  to  the  sides  of 
the  oesophagus  and  to  those  of  the  pericardium,  thus  consti- 
tuting a  rudimentary  diaphragm  ;  which,  it  will  be  observed, 
is  situated  in  front  of  the  lungs,  and  not  behind  them,  as  in 
the  higher  animals. 

Thus,  in  the  trunk,  on  the  ventral  side  of  the  vertebral 
column,  the  body  presents  two  cavities,  one  large  posterior 
pleuroperitoneal  cavity,  and  one  small,  anterior  to  the  fore- 
going, the  pericardial  cavity,  and  neither  of  these  communi- 
cates directly  with  the  exterior,  though  in  the  female  there 
is  an  indirect  communication  by  the  oviducts. 

'On  the  ventral  side  of  the  head,  the  very  wide  mouth 
opens  into  a  spacious  buccal  cavity,  the  roof  of  which  is  hard 
and  firm,  while  the  floor  is  soft  and  flexible,  except  so  far  as 
the  middle  of  it  is  occupied  by  a  broad,  flat,  for  the  most 
part  gristly  plate,  the  body  of  the  hyoid  bone.  Within  the 
lips  the  upper  jaw  is  beset  with  numerous  sharp  small  teeth, 
and  two  clusters  of  similar  teeth  are  to  be  seen  in  the  fore 
part  of  the  roof  of  the  mouth;  the  latter,  being  attached  to 
the  bones  termed  the  vomers,  are  the  vamerine  teeth,  while 
the  former,  attached  to  the  premaxillce  and  maxillce,  are 
maxillary  teeth.  The  lower  jaw  or  mandible  bears  no  teeth. 

At  the  sides  of  the  clusters  of  vomerine  teeth  are  the 
apertures  termed  posterior  nares,  by  which  the  nasal  chambers 
communicate  with  the  mouth.  At  the  sides  of  the  back  part 
of  the  throat  two  wide  passages,  the  Eustachian  recesses,  lead 


XIIL]  THE  FROG.  167 

into  the  tympanic  cavities,  which  are  closed  externally  by  the 
tympanic  membranes.  In  the  male  Rana  esculenta  the  small 
apertures  of  the  vocal  sacs  are  seen  on  the  inner  side  of  each 
ramus  of  the  jaw,  close  to  the  angle  of  the  gape  and  nearly 
opposite  the  Eustachian  recesses.  In  the  middle  of  the  back 
of  the  throat  is  the  opening  of  the  cesophagus,  closed  by  the 
approximation  of  its  sides  except  during  deglutition,  while  in 
the  median  line  of  the  hinder  part  of  its  floor  lies  a  longitu- 
dinal slit,  the  glottis.  A  fleshy  tongue,  bifurcated  and  free 
at  its  posterior  end,  is  attached  anteriorly  to  the  middle  part 
of  the  lower  jaw.  In  a  state  of  rest,  therefore,  it  lies  on  the 
floor  of  the  mouth  with  its  free  end  turned  backwards,  and 
one  point  on  each  side  of  the  glottis. 

The  gullet,  after  traversing  the  diaphragm,  passes  into  the 
elongated  stomach.  At  its  posterior  end  this  narrows  and 
joins  the  slender  small  intestine.  Though  short,  this  is  too 
long  relatively  to  the  length  of  the  abdominal  cavity  to  lie 
straight  in  it.  It  is,  therefore,  thrown  into  sundry  folds 
which  are  suspended  to  the  dorsal  -wall!  of  that  cavity  in  the 
manner  before  described.  Finally,  the  small  intestine  enters 
the  suddenly  dilated  short  large  intestine,  and  this  opens  into 
a  chamber  with  muscular  walls,  the  cloaca,  the  external  aper- 
ture of  which  has  been  already  mentioned. 

Thus  the  alimentary  canal  is  a  tube  which  traverses  the 
body  from  the  oral  to  the  anal  apertures;  and  the  heart,  en- 
closed in  the  pericardium,  is  situated  in  the  middle  line  on 
the  ventral  side  of  the  alimentary  canal. 

Separated  from  the  pleuroperitoneal  and  oral  cavities  by 
the  bodies  of  the  vertebrae  and  the  hard  roof  of  the  oral 
chamber  which  continues  the  direction  of  these  forwards,  is 
an  elongated  cavity,  widest  in  the  head  but  becoming  very 
narrow  posteriorly,  which  is  closed  on  all  sides  by  the  bony 
and  other  elements  of  the  head  and  spinal  column.  This  is 


r68  ELEMENTARY  BIOLOGY.  [CHAP. 

the  neural  cavity  and  contains  the  brain  and  spinal  cord, 
which  together  constitute  the  cerebro-spinal  nervous  axis.  The 
neural  cavity  is  lined  by  a  serous  membrane  resembling  the 
peritoneum  and  the  pericardium,  and  this  arachnoid  mem- 
brane is  reflected  on  to  and  covers  the  contained  cerebro- 
spinal  axis,  so  that  the  latter  is  related  to  it  as  the  heart  is  to 
the  pericardial  membrane. 

The  cerebro-spinal  nerves  which  are  given  off  from  the 
brain  and  spinal  cord  pass  to  their  destination  through  the 
boundary  walls  of  the  neural  cavity. 

A  transverse  section  of  the  head  in  the  region  of  the  eyes 
will  shew,  in  the  middle  line,  a  dorsal  cavity  in  which  the 
anterior  part  of  the  cerebro-spinal  axis,  the  brain,  is  con- 
tained, separated  by  the  solid  floor  of  the  skull  from  a 
ventral  cavity,  the  mouth. 

A  transverse  section  of  the  abdomen  will  shew  a  dorsal 
cavity  containing  the  posterior  part  of  the  cerebro-spinal 
axis,  the  spinal  cord,  separated  by  the  solid  floor  of  the  ver- 
tebral column  from  a  ventral  cavity  containing  the  ali- 
mentary canal  and  continuous  with  that  of  the  mouth. 
But  the  backward  continuation  of  the  alimentary  canal  is 
embraced  by  the  large  pleuroperitoneal  chamber,  of  which 
there  is  no  indication  in  the  head. 

On  comparing  the  transverse  section  of  the  abdomen  of 
the  Frog  with  a  transverse  section  of  the  middle  of  the  body 
of  the  Lobster,  it  will  be  seen  that  while  the  chief  nervous 
centre  is  on  one  side  of  the  alimentary  canal  and  the  heart 
on  the  opposite  side  in  both  cases,  there  is  no  solid  and  com- 
plete partition  between  the  nervous  centre  of  the  Lobster 
and  the  alimentary  canal.  Moreover,  the  face  of  the  body 
on  which  the  nervous  centre  lies,  is  that  on  which  the  Lobster 
naturally  rests,  while  in  the  Frog  it  is  the  reverse.  The 
limbs  are  turned  towards  the  neural  side  in  the  Lobster  and 


xiii.]  THE  FROG.  169 

away  from  it  in  the  Frog,  and  the  like  difference  obtains 
between  all  Vertdrata  and  all  Arthropoda. 

Using  the  term  skeleton,  in  its  broadest  sense,  for  the 
framework  which  protects,  supports  and  connects  the  various 
parts  of  the  organism,  it  consists  in  the  Frog  of  four  kinds  of 
tissue;  the  Horny,  the  Osseous,  the  Cartilaginous  and  the 
Connective.  Moreover,  the  hard  parts  are  either  developed 
in  the  integument,  constituting  an  exoskeleton^  or  they  are 
deeper  seated  and  belong  to  the  endoskeleton. 

Leaving  aside  a  question  that  may  arise  as  to  the  nature 
of  some  of  the  cranial  bones,  the  exoskeleton  in  the  Frog  is 
almost  absent,  being  represented  only  by  the  .horny  coating 
of  the  calcar. 

The  endoskeleton,  on  the  contrary,  is  well  developed  and, 
as  in  all  the  higher  Vertebrata,  may  be  distinguished  into  an 
axial  and  an  appendicular  portion. 

The  axial  endoskeleton  consists  of  the  notochord,  the  spinal 
column  and  the  skull. 

The  appendicular  endoskeleton  occurs  in  the  limbs  and  in 
the  pectoral  and  pelvic  arches  to  which  they  are  attached. 

In  the  order  of  development,  the  endoskeleton  is  at  first 
represented  by  the  notochord  alone;  secondly,  nascent  con- 
nective tissue  and  cartilage  are  superadded  to  the  notochord; 
thirdly,  these  acquire  their  special  characters;  fourthly,  they 
become  replaced  by. bone. 

The  process  of  conversion  or  replacement  indicated  under 
the  last  head  is  very  incomplete,  even  in  the  adult  Frog, 
in  which  remains  of  the  notochord  are  to  be  found  in  the 
centres  of  the  vertebrae;  and  the  cartilage,  of  which  the 
greater  part  of  the  skeleton  at  one  period  of  larval  ex- 
istence was  composed,  to  a  great  extent  persists. 

Such  cartilage  is  found  forming  the  free  surfaces  of  the 


1 70  ELEMENTARY  BIOLOGY.  [CHAP. 

bodies  of  the  vertebrae,  the  extremities  of  the  caudal  style 
(iirostyle}  and  the  ends  of  the  transverse  processes;  and  it 
enters  largely  into  the  sternum.  In  the  skull,  the  para- 
sphenoid1,  vomers,  parieto-frontals,  nasals,  premaxillae,  max- 
illae, jugals,  squamosals,  and  the  bony  elements  of  the  man- 
dible may  be  removed  by  maceration,  leaving  behind  the 
primitive  cartilaginous  skull,  or  Chondro-cranium,  altered  only 
so  far  as  parts  of  it  have  been  replaced  by  bone. 

It  furnishes  a  floor,  side  walls  and  roof  to  the  brain-case, 
interrupted  only  by  a  large  space  (called  &fontanelle)  covered 
in  by  membrane,  which  lies  in  the  inter-orbital  region  under 
the  parieto-frontals,  and  by  the  foramina  for  the  exit  of  the 
cranial  nerves.  It  consists  entirely  of  cartilage,  except  where 
the  exoccipitals,  the  pro-otics,  and  the  sphenethmoid  invade 
its  substance.  In  front  of  the  septum  of  the  anterior  cavity 
of  the  sphenethmoid,  it  is  continued  forward  between  the 
two  nasal  sacs,  as  the.  cartilaginous  partition  between  the 
nasal  cavities  (septum  narium),  from  which  are  given  off, 
dorsally  and  ventrally,  transverse  alse  of  cartilage  which  fur- 
nish a  roof  and  a  floor,  respectively,  to  'the  nasal  chambers. 
Of  these,  the  floor  is  the  wider.  The  dorsal  and  ventral  alae 
pass  into  one  another  where  the  chondro-cranium  ends  an- 
teriorly and  give  rise  to  a  truncated  terminal  face,  which  is 
wide  from  side  to  side,  narrow  from  above  downwards,  and 
convex  in  the  latter  direction.  The  lateral  angles  of  this 
truncated  face  are  produced  outwards  and  forwards  into  two 
flatten z&  pra-nasal  processes  ;  these  widen  externally  and  end 
by  free  edges  which  support  the  adjacent  portions  of  the 
premaxillae  and  maxillae.  From  the  ventral  face,  just  behind 
the  truncated  anterior  end  of  the  chondro-cranium,  spring 

1  See  Laboratory  work,  D,  c,  for  the  structure  of  the  bony  skull 
(osteocraniuni],  which  should  be  thoroughly  understood  before  any 
attempt  is  made  to  study  the  cartilaginous  skull  or  chondro-cranium. 


XIIL]  THE  FROG.  171 

two  slender  cartilages,  the  rhinal  processes.  Each  of  these 
inclines  towards  the  middle  line  and  ends  against  the  middle 
of  the  posterior  face  of  the  ascending  process  of  the  pre- 
maxilla  by  a  vertically  elongated  extremity.  An  oval  nodule 
of  cartilage  is  attached  to  the  posterior  face  of  the  dorsal 
end  of  the  ascending  process  of  the  premaxilla,  and  serves 
to  connect  it  with  the  rhinal  process.  On  the  dorsal  face  of 
the  chondro-cranium,  just  above  the  point  of  attachment  of 
the  rhinal  processes,  the  external  nasal  apertures  are  situated, 
and  the  outer  and  posterior  margins  of  each  of  these  aper- 
tures are  surrounded  and  supported  by  a  curious  curved 
process  of  the  cartilaginous  ala — the  alinasal process.  Where 
the  sphenoidal  and  the  ethmoidal  portions  of  the  spheneth- 
moid  meet,  a  stout,  transverse,  partly  osseous  and  partly 
cartilaginous  bar  is  given  off,  which  is  perforated  at  its  origin 
by  the  canal  for  the  orbito-nasal  nerve.  It  then  narrows, 
but  becoming  flattened  from  above  downwards,  rapidly 
widens  again,  and  its  axe-head-like  extremity  abuts  against 
the  inner  face  of  the  maxilla.  The  anterior  angle  of  the 
axe-head  is  free;  the  posterior  angle  is  continued  back  into 
a  slender  cartilaginous  pterygoid  rod  which  bifurcates  poste- 
riorly. The  outer  division  passes  into  the  ventral  crus  of 
the  suspensorium.  The  inner  division  is  the  pedicle  of  the 
suspensorium;  it  articulates  by  a  joint  with  the  anterior  face 
of  the  broad  lateral  process  of  the  hinder  part  of  the  chon- 
dro-cranium, which  contains  the  auditory  labyrinth  and  is 
termed  the  periotic  capsule.  The  Suspensorium  is  a  rod  of 
cartilage,  which  lies  between  the  squamosal  and  the  ptery- 
goid bones  and,  at  its  distal  end,  articulates  with  Meckefs 
cartilage  which  forms  the  core  of  the  ramus  of  the  mandible. 
At  its  dorsal  end  it  divides  into  two  divergent  processes  or 
crura,  of  which  the  ventral  crus  has  already  been  said  to  be 
continuous  with  the  pterygoid.  The  dorsal  crus,  on  the 


172  ELEMENTARY  BIOLOGY.  [CHAP. 

other  hand,  passes  upwards  and,  curving  backwards,  becomes 
attached  to  the  dorsal  part  of  the  outer  face  of  the  periotic 
capsule. 

Meckel's  cartilage,  articulated  to  the  free  end  of  the  sus- 
pensorium,  is  unossified  throughout  the  greater  part  of  its 
extent,  no  osseous  articulare  being  developed;  but,  at  its 
symphysial  end,  each  cartilage  becomes  ossified,  and  forms 
the  mento-Meckelian  element  of  the  mandible. 

The  slender,  cartilaginous  band  (cornu  of  the  hyoiff)  by 
which  the  body  of  the  hyoid  is  attached  to  the  skull,  is  con- 
nected with  the  periotic  cartilage  immediately  in  front  of 
and  below  the  fenestra  ovalis. 

The  pectoral  and  pelvic  arches  (see  Laboratory  work 
D.  e.  g.)  are,  in  the  young  state,  undivided  cartilages  on 
each  side,  and  the  development  of  bone  in  and  upon  them 
does  not  really  destroy  this  continuity,  the  cartilage  persist- 
ing at  the  ends  of  the  bones  and  between  them,  in  the 
glenoidal  and  acetabular  cavities. 

In  like  manner,  the  bones  of  the  limbs  consist  origin- 
ally of  merely  cartilaginous  models  of  the  perfect  bone; 
but,  as  development  proceeds,  the  middle  of  the  cartilagi- 
nous model  commonly  becomes  invested  by  a  sheath  of 
true  bone,  while  a  calcareous  deposit  takes  place  in  the 
cartilage  close  to  its  growing  extremities.  As  the  bone 
grows,  the  superadded  sheath  invades  the  middle  of  the 
cartilage  and  more  or  less  replaces  it;  while  the  terminal 
portions  of  cartilage  continue  to  grow  and  enlarge  and  the 
calcareous  deposit  within  them  increases,  without  however 
reaching  their  surfaces.  Thus  one  of  the  larger  adult  limb- 
bones,  the  femur,  consists  of  a  median  shaft  of  perfect  bone, 
and  of  two  terminal  cones  of  cartilage,  containing  calcified 
epiphyses,  enclosed  within  and  more  or  less  overlapping  the 
hollow  ends  of  the  shaft. 


xni.]  THE  FROG.  173 

The  general  disposition  of  the  parts  which  are  seen  in 
the  mouth  has  already  been  described. 

Teeth  are  found  attached  only  to  the  premaxillse,  max- 
illae and  vomers.  They  are  small,  with  recurved  and 
pointed  crowns.  New  teeth  are  constantly  being  developed 
in  the  gum  to  replace  those  which  are  worn  out  or  broken 
away.  And  as  they  attain  their  full  size  these  teeth  be- 
come ankylosed  to  processes  of  the  subjacent  bone. 

The  gullet  passes  without  change  of  diameter  into  the 
stomach,  which  lies  on  the  left  side  of  the  abdominal  cavity 
and  is  nearly  as  long  as  it.  The  stomach  narrows  poste- 
riorly and  the  almost  tubular  pyloric  portion  bends  round 
sharply  and  passes  into  the  duodenum.  A  slight  constric- 
tion marks  the  pylorus.  The  duodenum  runs  forwards 
parallel  with  the  stomach,  so  that  with  the  latter  it  forms  a 
sort  of  loop.  At  its  anterior  end  it  passes  into  the  rest  of 
the  small  intestine  (ileum),  which  is  coiled  up  into  a  sort  of 
packet  and  lies  on  the  right  side  of  the  abdominal  cavity, 
being  held  in  its  place  by  a  mesenteric  fold  of  the  perito- 
neum. From  the  comparatively  narrow  neck  of  the  packet, 
the  small  intestine  proceeds  backwards  in  the  middle  line 
and  opens  into  the  anterior  end  of  the  dilated  large  intes- 
tine or  colon  and  rectum. 

The  inner  wall  of  the  stomach  is  raised  up  into  a  number 
of  strong  longitudinal  folds  which  project  into  its  cavity 
and  give  it  a  stellate  appearance  in  transverse  section. 
Much  more  delicate  continuations  of  these  folds  are  conti- 
nued into  the  small  intestine  and  are  there  joined  by  trans- 
verse folds. 

The  opening  of  the  ileum  into  the  colon  is  valvular,  its 
edges  projecting  backwards  into  the  cavity  of  the  colon. 
On  the  dorsal  aspect,  this  presents  a  slight  forward  dilata- 
tion, which  may  be  regarded  as  a  rudiment  of  a  caecum. 


174  ELEMENTARY  BIOLOGY.  [CHAP. 

The  liver  is  very  large,  and  is  divided  into  two  lobes 
united  by  a  mere  bridge,  dorsally  and  anteriorly.  The  left 
lobe  is  further  subdivided  into  two.  The  gall  bladder  is 
attached  to  the  posterior  and  dorsal  face  of  the  right  lobe. 
The  biliary  duct  opens  into  the  duodenum,  at  some  distance 
behind  the  pylorus,  and  its  termination  is  embraced  by  the 
base  of  the  slender  pancreas. 

The  rounded  spleen  lies  in  the  mesentery,  projecting 
more  to  the  left  than  to  the  right  side,  just  above  the  point 
at  which  the  duodenum  passes  into  the  ileum. 

The  apparatus  of  circulation  in  the  Frog  consists  of  the 
blood  and  lymph  vessels  and  their  contents. 

The  lymph  is  a  colourless  fluid  containing  colourless 
nucleated  corpuscles  which  exhibit  amoeboid  movements : 
it  is  contained  partly  in  large  spaces  immediately  beneath 
the  integument;  in  the  pleuroperitoneal  cavity  and  pro- 
bably in  the  other  serous  cavities;  and,  partly,  in  capillaries 
and  larger  trunks  which  are  interlaced  with  and  accompany 
the  blood-vessels.  The  largest  of  the  trunks  is  the  great 
sub-vertebral  lymph-sinus,  which  lies  between  the  layers  of 
the  root  of  the  mesentery  and  communicates  by  small  pores 
with  the  pleuroperitoneal  cavity.  There  are  four  lymph- 
hearts. 

The  blood  consists  of  a  colourless  plasma  which  contains 
colourless  corpuscles,  similar  to  those  of  the  lymph,  and  in 
addition  a  great  number  of  oval  nucleated  red  corpuscles. 
It  is  contained  in  the  blood-vessels,  which  consist  of  capil- 
laries, arteries  and  veins,  the  two  latter  being  connected  on 
the  one  side  by  the  capillaries  and,  on  the  other,  by  the 
heart  into  which  they  open.  The  lymphatics  and  the 
blood  vessels  are  brought  into  connexion  with  one  another 
by  communications  between  the  anterior  lymph-hearts  and 


xin.]  THE  FROG.  175 

the  innominate  veins,  and  between  the  posterior  lymph- 
hearts  and  the  iliac  veins. 

The  heart  is  connected  with  the  walls  of  the  pericardium, 
on  which  spots  of  pigment  may  be  observed,  by  the  vessels 
which  enter  and  leave  it,  and  by  a  slender  band  which 
passes  from  the  dorsal  face  of  the  base  of  the  ventricle  to 
the  posterior  and  dorsal  wall  of  the  pericardial  chamber. 

The  heart  consists  of  four  readily  distinguishable  seg- 
ments, (i)  the  sinus  venosus,  (2)  the  atrium,  (3)  the  ven- 
tricle, and  (4)  the  truncus  arteriosus,  disposed  in  such  a 
manner  that  the  sinus  venosus,  which  is  the  hindermost 
division,  lies  in- the  middle  line  on  the  dorsal  aspect  of  the 
heart:  the  atrium  is  also  median  and  on  the  dorsal  side, 
but  is  in  front  of  the  sinus  venosus;  the  ventricle  is  me- 
dian, ventral  and  posterior;  and  the  truncus  passes  ob- 
liquely forwards  from  the  right  side  of  the  ventricle  and  is 
ventral  and  anterior.  The  heart  therefore  may  be  com- 
pared to  a  tube  divided  by  constriction  into  four  portions 
and  bent  somewhat  into  the  shape  of  an  S. 

The  sinus  venosus  receives  on  each  side,  in  front,  a  large 
vein,  the  vena  cava  superior;  while  behind  the,  usually  sin- 
gle, vena  cava  inferior  opens  into  it.  It  opens  by  a  valvu- 
lar aperture  into  the  atrium.  The  latter  shews  no  signs  of 
division  externally,  but,  internally,  it  is  divided  by  a  deli- 
cate partition,  the  septum-  of 'the  auricles,  into  a  smaller  left 
auricle  and  a  larger  right  auricle.  The  sinus  venosus  opens 
into  the  atrium,  to  the  right  of  the  septum  and  therefore 
into  the  right  auricle.  Into  the  left  auricle,  the  common 
pulmonary  vein,  a  small  trunk  formed  by  the  junction  of  the 
veins  from  the  right  and  left  lungs,  opens. 

At  its  posterior  end  the  atrium  opens  by  the  auriculo- 
ventricular  aperture  into  the  ventricle. 

A  small  valve,  prevented  from  flapping  back  by  fine  ten- 


J76  ELEMENTARY  BIOLOGY.  [CHAP. 

dinous  cords,  exists  on  each  side  of  this  aperture,  and  the 
septum  of  the  auricles  is  continued  back  upon  the  faces  of 
these  valves  and  ends  by  a  free  edge  between  them,  thus 
dividing  the  auriculo-ventricu  lar  aperture  itself  into  two 
openings. 

The  walls  of  the  sinus  and  of  the  atrium  are  very  thin. 
Those  of  the  ventricle,  on  the  other  hand,  are  thick  and 
spongy,  only  a  comparatively  small,  transversely  elongated, 
clear  cavity  being  left  at  the  anterior  end  or  base  of  the 
ventricle.  At  the  right  extremity  of  this  is  the  aperture 
which  leads  into  the  truncus  arteriosus.  Three  semilunar 
valves,  which  open  from  the  ventricle  into  the  truncus,  sur- 
round this  opening. 

The  walls  of  the  truncus  arteriosus  are  thick  and  mus- 
cular, though  not  nearly  so  thick  as  those  of  the  ventricle. 
At  its  anterior  end  it  appears  to  divide  into  two  trunks, 
which  diverge  and  immediately  leave  the  pericardium  to 
pass  on  to  the  sides  of  the  gullet.  The  elongated  undi- 
vided part  is  the  pylangium,  the  terminal  part  common  to 
the  divergent  trunks  is  the  synangium.  The  former  is 
divided  throughout  its  length  by  a  sort  of  fold  which  is 
attached  to  the  dorsal  wall  while  its  opposite  edge  is  free. 
Three  semilunar  valves  separate  the  pylangium  from  the 
synangium,  in  which  are  the  openings,  posteriorly,  of  the 
pulmonary  arteries,  anteriorly  of  the  carotid  trunks;  while, 
at  the  sides,  the  cavity  of  the  synangium  opens  into  those 
of  the  right  and  left  aortic  arches.  The  apparently  simple 
branches  into  which  the  truncus  arteriosus  divides,  are,  in 
fact,  each  made  up  of  three  separate  trunks,  the  pulmo- 
cutaneous  trunk  behind,  the  aortic  arch  in  the  middle  and 
the  carotid  trunk  in  front. 

When  the  heart  is  in  action,  the  sinus  venosus,  the  atrium, 
the  ventricle  and  the  truncus  arteriosus  contract  in  the 


XIIL]  THE  FROG.  177 

order  in  which  they  have  just  been  named.  Each  contracts 
as  a  whole,  so  that  the  two  auricles  are  emptied  simulta- 
neously. The  blood  from  each  is  forced  into  the  correspond- 
ing half  of  the  spongy  cavity  of  the  ventricle,  so  that  the 
right  half  of  the  ventricle  contains  venous  blood  and  the 
left  arterial  blood.  When  the  systole  of  the  ventricle  takes 
place,  the  blood  which  is  first  driven  into  the  truncus  arte- 
riosus  (the  opening  of  which  is,  as  has  been  seen,  at  the 
right  end  of  the  cavity)  is  therefore  venous.  It  fills  the 
conus  arteriosus  and,  finding  least  resistance  in  the  short 
and  wide  pulmonary  vessels,  passes  along  the  left  side  of  the 
median  valve  into  them.  But  as  they  become  distended 
and  less  resistance  is  offered  elsewhere,  the  next  portion 
of  blood,  consisting  of  the  venous  and  arterial  blood  which 
have  become  mixed  in  the  middle  of  the  ventricle,  passes  on 
the  right  side  of  the  longitudinal  valve  into  the  aortic  arches. 
And,  as  the  truncus  becomes  more  and  more  listen ded,  the 
longitudinal  valve,  flapping  over,  tends  more  and  more 
completely  to  shut  off  the  openings  of  the  pulmonary 
arteries  and  to  prevent  any  blood  from  flowing  into  them. 

Finally,  the  last  portion  of  blood  from  the  ventricle, 
representing  the  completely  arterialized  blood  of  the  left 
auricle  which  is  the  last  to  arrive  at  the  opening  of  the 
truncus,  passes  into  the  carotid  trunks  and  is  distributed  to 
the  head. 

The  principal  vessels  of  the  Frog  are  disposed  as  fol- 
lows : — 

A.     Arteries. 

i.     The   system    of    the   anterior    aortic   arch    (carotid 
trunk). 

a.     Lingual  artery — to  the  tongue. 
M.  12 


178  ELEMENTARY  BIOLOGY.  [CHAP. 

b.      Carotid  artery — to  the  interior  of  the  skull  and 
the  brain. 

2.  The  system  of  the  middle  aortic  arch  (aortic  trunks). 

a.  Vertebral  and  sttbclavian — to  the  vertebral  co- 
lumn, and  to  the  fore-limb.     (Esophageal  to  the 
gullet. 

b.  Coiliaco-mesenteric  (given  off  from  the  left  arch, 
or  from  the  dorsal  aorta,  at,  or  beyond,  the  junc- 
tion of  the  two  arches). 

a.     Cceliac  to  stomach  and  liver, 

13.     Mesenteric  to  intestine  and  spleen. 

c.  Branches   of  the   dorsal  aorta  to   the  adrenal 
and  renal  organs,  to  the  genital  organs  and  to 
the  muscles  of  the  back. 

d.  The  terminal  branches  of  the  dorsal  aorta  (com- 
mon iliac) ;   each  of  these  gives  off  hypogastric 
arteries  to  the  bladder  and  walls  of  the  abdomen 
and  is  continued  as  the  femoral  artery  into  the 
leg. 

3.  The    system    of   the    posterior  aortic   arch    (pulino- 
cutaneous  trunk). 

a.  Pulmonary  artery  to  the  lungs. 

b.  Cutaneous  artery  to  the  dorsal  integument. 

B.      Veins. 

i.  The  system  of  the  superior  cava  formed  on  each 
side  by  the  union  of  the  vena  innominata,  the  sub- 
clavian  and  the  external  jugular. 

a.      Internal  jiignla*-  vein:   leaves  the  skull  by  the 
jugular  foramen,  and  brings  back  blood  from 


XIII.] 


THE  FROG. 


179 


the  brain,  spinal  cord   and   anterior  vertebral 
region. 

b.  Subscapular :  returns  the  blood  from  the  bra- 
chium  and  shoulder.     These  two  veins  (a.  and 
b.)  unite  to  form  the  vena  innominata. 

c.  The  musculo-cutaneous  vein,  receiving  the  blood 
of  the  surface  of  the  head  (except  the  mandi- 
bular  and  hyoidean  regions)   and  that   of  the 
back  of  the  trunk — passes  forwards  between  the 
internal  and  external  oblique  muscles   of  the 
abdomen. 

d.  The  bratfiial  vein  receives  blood  from  the  ante- 
brachium  and  manus. 

These  (c.  and  d.)  unite  to  form  the  subclavian 
vein. 

e.  The  veins  of  the  mandibular  region  and  those 
of  the  tongue  unite  into  the  external  jugular 
vein. 

2 .     The  system  of  the  inferior  cava,  formed  by  the  union 
of  the  renal,  genital  and  hepatic  veins. 

a.  The  femoral  vein  from  the  front  of  the  leg, 
and — 

b.  The  sciatic  vein  from  the  back  of  the  leg,  pour 
their  blood  into  a  trunk  which  lies  in  the  lateral 
wall  of  the  pelvis  and  may  be  termed  the  pelvic 
vein;  the  dorsal  end  of  this  becomes — 

c.  The  common  iliac  vein,  which  passes  to  the  outer 
edge  of  the  kidney  and  is  distributed  to  that 
organ,  whence  the  blood  is  carried  to  the  vena 
cava  inferior  by  the  renal  veins. 

12 — 2 


i8o  ELEMENTARY  BIOLOGY.  [CHAP. 

d.  The  dorso-lumbar  vein,  which  lies  along  the 
transverse  processes  of  the  vertebrae  and  receives 
blood  from  the  walls  of  the  abdomen  and  from 
the  interior  of  the.  spinal  canal,  opens  into  the 
common  iliac. 

3.  The  system  of  the  anterior  abdominal  vein,  formed 
by  the  union  of  the  ventral  ends  of  the  pelvic  veins 
(2.  b.).     It  receives  blood  from  the  urinary  bladder 
and  the  walls  of  the  abdominal  cavity,  and  at  its 
anterior  end  divides  into  two  branches — a  right  and 
a  left.     These  branches   go  to  the   corresponding 
lobes  of  the  liver,  the  left  receiving  a  large  commu- 
nicating branch  from  the  gastric  division  of  the  vena 
portce. 

4.  The  system  of  the  vena  portce  formed  by  the  union 
of  two  veins;  one,  gastric,  which  brings  back  the 
blood  from  the  stomach,  the  other,  lieno-intestinal, 
which  returns  that  from  the  spleen  and  intestines. 

[Hence  the  right  lobe  of  the  liver  and  part  of  the  left 
lobe  are  supplied  with  systemic  venous  blood,  more 
or  less  mixed  with  gastric  venous  blood,  while  only  part 
of  the  left  lobe  is  supplied  with  intestinal  venous  blood. 
Besides  this  venous  blood,  it  must  be  recollected  that 
the  liver  receives  arterial  blood  by  the  hepatic  artery.] 

5.  The  system  of  the  pulmonary  vein,  formed  by  the 
union  of  the  veins  of  the  right  and  left  lungs. 

In  addition  to  the  apparatus  of  the  circulation  of  the 
blood,  the  Frog  possesses  two  pairs  of  lymph-hearts.  These 
are  contractile  muscular  sacs,  which  are  connected  on  the 
one  hand  with  the  lymphatic  vessels  and  on  the  other  with 
large  veins  in  their  neighbourhood;  and  which  pump  the 


xni.]  THE  FROG.  181 

lymph  contained  in  the  wide  lymphatic  vessels  and  in  the 
pleuro-peritoneal  cavity  of  the  Frog,  into  these  veins. 

The  anterior  lymph-hearts  are  situated  close  to  the  trans- 
verse processes  of  the  third  vertebra,  below  the  edge  of  the 
scapula;  the  posterior  pair  lie  one  on  each  side  of  the  uro- 
style,  and  their  pulsations  may  be  observed  by  carefully 
watching  the  integument  in  this  region  in  a  living  Frog. 

The  Thymus  gland  is  a  small  rounded  body  situated  im- 
mediately behind  the  suspensorium,  in  a  position  corre- 
sponding to  the  dorsal  ends  of  the  obliterated  branchial 
arches. 

The  Thyroid  gland  appears  to  be  represented  by  two  or 
more  oval  bodies,  which  are  found  attached  to  the  lingual 
vessels  and  between  the  aortic  and  pulmo-cutaneous  trunks. 

The  Adrenal  glands  are  yellow  bodies  imbedded  in  the 
ventral  face  of  the  kidney. 

The  slit-like  glottis  of  the  Frog  is  formed  by  the  apposi- 
tion of  two  longitudinal  folds  of  the  mucous  membrane  of 
the  mouth,  each  of  which  contains  a  cartilage  of  similar 
form.  These  cartilages  are  the  arytenoid  cartilages.  They 
are  articulated  with  an  annular  cartilage  (laryngo-tracheat) 
which  supports  the  wall  of  the  very  short  chamber  which 
represents  the  larynx  and  trachea.  When  the  two  folds  of 
the  glottis  are  divaricated,  there  are  seen  between  them  two 
membranous  pouches,  the  free  edges  of  which  meet  in  the 
middle  line,  while  anteriorly  and  posteriorly  they  pass  into 
the  mucous  membrane  which  lines  the  faces  of  the  longitu- 
dinal folds.  These  are  the  vocal  ligaments,  and  the  slit 
between  them  is  what  answers  to  the  glottis  in  Man.  It 
is  by  their  vibration  that  the  croak  of  the  Frog  is  produced. 

Laterally  the  laryngo-tracheal  chamber  opens  into  the 


182  ELEMENTARY  BIOLOGY.  [CHAP. 

lung  of  each  side.  The  lung  is  a  transparent  oval  sac, 
somewhat  pointed  posteriorly,  which  lies  at  the  side  of  the 
oesophagus  in  the  dorsal  region  of  the  abdominal  cavity. 
It  is  covered  by  a  layer  of  the  pleuroperitoneal  membrane 
which  represents  the  visceral  layer  of  the  pleura  in  the 
higher  animals.  The  wall  of  the  pulmonary  sac  is  pro- 
duced inwards  so  as  to  give  rise  to  septa,  which  are  much 
more  prominent  and  more  numerous  in  the  anterior  than 
in  the  posterior  part  of  the  lung  and  divide  the  periphery 
of  the  cavity  into  numerous  air-cells,  on  the  walls  of  which 
the  ramifications  of  the  pulmonary  artery  are  distributed. 

The  lungs  are  elastic,  the  distended  lung  collapsing  sud- 
denly when  it  is  pricked,  and  they  contain  abundant  mus- 
cular fibres. 

Inspiration  is  effected  in  the  Frog  by  a  buccal  force- 
pump.  The  mouth  being  shut  and  the  external  nostrils 
open,  the  floor  of  the  mouth  is  depressed,  and  the  buccal 
cavity  fills  with  air.  The  nostrils  being  then  shut,  the 
hyoid,  and  with  it  the  floor  of  the  mouth,  is  raised,  the 
aperture  of  the  gullet  being  at  the  same  time  closed.  Thus 
the  air  is  forced  through  the  glottis  and  distends  the  lungs. 

In  ordinary  expiration,  the  elasticity  of  the  lungs  and 
the  pressure  of  the  surrounding  viscera  probably  suffice  to 
expel  the  air;  but  this  operation  may  be  powerfully  aided, 
firstly  by  the  contraction  of  the  intrinsic  muscular  fibres  of 
the  lungs;  secondly,  by  the  contraction  of  the  muscles  of 
the  lateral  and  ventral  regions  of  the  abdominal  wall;  and, 
thirdly,  by  the  contraction  of  those  muscular  fibres  which 
enter  into  the  diaphragm ;  as  all  these  actions  tend,  either 
directly  or  indirectly,  to  diminish  the  capacity  of  the  lungs. 

It  is  essential  to  inspiration  that  the  mouth  should  be 
shut,  and  it  is  said  that  frogs  may  be  asphyxiated  by  keeping 
their  mouths  open. 


xiii.]  THE  FROG.  183 

In  addition  to  its  principal  pulmonary  apparatus  of  re- 
spiration, the  Frog  has  a  secondary  respiratory  apparatus  in 
its  moist  and  delicate  skin.  A  considerable  amount  of  venous 
blood  is,  in  fact,  constantly  supplied  to  this  organ  by  the 
large  cutaneous  branch  of  the  pulmo-cutaneous  artery.  It 
has  been  experimentally  ascertained  that  frogs  in  which  the 
lungs  have  been  extirpated  will  continue  to  live  and  respire 
for  a  considerable  time,  especially  at  a  low  temperature,  by 
means  of  the  skin. 

The  kidneys  are  elongated  and  flattened  from  side  to  side, 
and  are  kept  in  their  places  by  the  continuation  of  the  peri- 
toneum over  their  ventral  faces.  The  ducts  of  the  kidneys 
pass  from  about  the  junction  of  the  middle  and  posterior 
thirds  of  the  outer  edge  of  each  kidney  and,  approaching  as 
they  pass  backwards,  open  by  two  small  closely  approxi- 
mated slit-like  apertures  in  the  posterior  wall  of  the  cloaca. 

The  urinary  bladder  is  a  large  bilobed  sac,  opening  pos- 
teriorly, by  a  wide  median  aperture,  into  the  anterior  end 
of  the  cloaca,  on  the  ventral  side  of  the  rectum. 

The  testes  are  spheroidal  yellowish  bodies  situated  in 
front  of  the  kidneys  and  enveloped  in  peritoneum,  a  fold  of 
which,  forming  a  sort  of  testicular  mesentery  or  mesorchium, 
passes  into  that  which  covers  the  ventral  face  of  the  kidney. 
The  delicate  vasa  efferentia  of  the  testes  may  be  seen  travers- 
ing this  fold  to  enter  the  substance  of  the  kidney.  They 
communicate  with  the  urinary  tubules,  and  thus  the  duct  of 
the  kidney  serves  not  only  as  the  duct  of  the  urinary  ex- 
cretion but  as  the  vas  defer  ens. 

The  spermatozoa  of  Rana  esculenta  have  thick  and  cylin- 
drical heads,  while  those  of  Rana  temporaria  are  linear. 

The  ovaria  are  broad  lamellar  organs,  very  large  and 
much  folded  and  plaited  in  the  breeding  season.  The  in- 


184  ELEMENTARY  BIOLOGY.  [CHAP. 

teripr  of  each  is  hollow,  and  is  divided  into  several  chambers. 
Innumerable  ovisacs,  containing  dark-coloured  ova,  are  scat- 
tered through  the  substance  of  the  ovary  and  give  rise  to 
projections  upon  the  inner  surface  of  the  ovarian  chamber 
as  they  -become  fully  developed. 

The  oviducts  are  long  convoluted  tubes  situated  on  each 
side  of  the  dorsal  wall  of  the  abdominal  cavity  to  which  they 
are  connected  by  peritoneal  folds ;  each  curves  over  the 
outer  face  of  the  root  of  the  lung.  Their  anterior  ends  are 
very  slender,  and  terminate  by  open  mouths  at  the  sides  of 
the  pericardium,  between  the  attachment  of  the  diaphragm 
and  the  lobe  of  the  liver.  The  fold  of  peritoneum  which 
serves  as  a  ligament,  holding  the  lobe  of  the  liver  to  the 
diaphragm,  oesophagus  and  posterior  wall  of  the  pericar- 
dium, in  fact  constitutes  the  outer  lip  of  the  oviducal  aper- 
ture. For  the  greater  part  of  their  length  their  walls  are 
thick  and  glandular,  and  swell  up  when  placed  in  water. 
Posteriorly,  the  oviducts  dilate  into  capacious  thin-walled 
chambers  and  end,  close  together,  by  openings  which  are 
situated  in  the  dorsal  wall  of  the  cloaca  immediately  in  front 
of  the  apertures  of  the  ureters, 

Each  ovum,  when  ripe,  consists  of  a  structureless  vitelline 
membrane,  inclosing  a  vitellus,  within  which  is  a  germinal 
vesicle,  containing  several  l  germinal  spots.'  One  half  of 
the  vitellus  is  deeply  coloured,  the  other  pale. 

The  actions  of  the  different  parts  of  the  organism  of  the 
Frog  are  coordinated  with  one  another  and  brought  into 
relation  with  the  external  world  by  means  of  the  muscular 
and  nervous  systems  and  the  organs  of  sense. 

The  muscles  consist  partly  of  striped  and  partly  of  un- 
striped  fibres,  the  former  being  confined  to  the  muscles  of 
the  head,  trunk  and  limbs  and  the  heart,  while  the  latter 


xin.  1  THE  FROG.  185 

are  found  in  the  viscera  and  vessels.  An  account  of  the 
disposition  of  the  muscles  in  the  hind-limb  will  be  found  in 
the  Laboratory  work. 

The  nervous  system  is  conveniently  divisible  into  two 
parts,  the  cerebro-spinal  and  the  sympathetic.  The  cerebro- 
spinal  nervous  system  again  consists  of  t3ie  brain,  or  encepha- 
lon,  with  its  nerves,  and  the  spinal  cord,  or  myelon,  with  its 
nerves. 

The  encephalon  lies  in  the  cranial  cavity,  which  it  nearly 
fills,  and  is  divisible  into  the  hind-brain,  the  mid-brain  and 
the  fore-brain,  which  last  again  comprises  three  divisions ; 
the  thalamencephalon,  the  cerebral  hemispheres,  and  the 
olfactory  lobes. 

The  greater  part  of  the  hind-brain  is  formed  by  the 
medulla  oblongata,  which  is  the  continuation  of  the  myelon 
forwards  and  presents,  on  its  dorsal  aspect,  a  triangular 
cavity,  the  apex  of  which  is  directed  backwards.  It  is  roofed 
over  by  a  thick  and  very  vascular  membrane  (choroid  plexus), 
the  inner  surface  of  which  presents  transverse  folds  on  either 
side  of  a  median  longitudinal  ridge.  The  cavity  is  the 
fourth  ventricle;  it  communicates  behind  with  the  central 
canal  of  the  myelon,  while,  in  front,  it  narrows  into  a  pas- 
sage which  connects  the  fourth  ventricle  with  the  cavities 
anterior  to  it.  The  thick  lateral  ridges  of  nervous  substance 
at  the  sides  of  the  fourth  ventricle,  which  represent  the 
restiform  bodies,  pass,  in  front,  into  the  outer  extremities  of 
a  short  broad  tongue-shaped  plate,  convex  ventrally  and 
concave  dorsally,  which  overhangs  the  anterior  part  of  the 
fourth  ventricle,  and  is  the  cerebellum. 

In  front  of  this,  the  dorsal  moiety  of  the  mid-brain  is 
formed  by  two  oval  bodies,  the  long  axes  of  which  are 
directed  inwards  and  backwards.  These  are  the  optic  lobes. 
When  laid  open,  each  is  seen  to  contain  a  cavity  or  ventricle 


i36  ELEMENTARY  BIOLOGY.  [CHAP. 

with  an  opening  on  its  inner  face.  These  openings  lead  into 
a  short  passage,  which  communicates  with  the  iter  a  tertio  ad 
quartum  ventriculum,  as  the  canal  which  leads,  through  the 
mesencephalon,  from  the  fourth  to  the  third  ventricle  is 
termed.  The  floor  of  this  canal  is  formed  by  the  thick  prin- 
cipal mass  of  the  cerebro-spinal  axis.  It  exhibits  a  median 
longitudinal  depression  or  raphe,  and  in  this  region  repre- 
sents the  cmra  cerebri. 

In  front  of  the  mid-brain  comes  the  hinder  division  of 
the  fore-brain,  or  thalamencephalon,  which  is  very  distinct  in 
the  Frog  and  contains  a  median  cavity,  the  third  ventricle. 
On  each  side,  the  cavity  of  the  third  ventricle  is  bounded 
by  a  thick  mass  of  nervous  matter  into  which  the  crura 
cerebri  pass.  These  are  the  optic  thalami.  Dorsally,  the 
walls  of  the  third  ventricle  are  very  thin  and  easily  torn 
through,  except  behind,  where  there  is  a  thick  transverse 
band  of  nervous  substance,  the  posterior  commissure. 

From  the  fore  part  of  the  roof  of  the  third  ventricle,  a 
delicate  process  proceeds  to  the  pineal  gland — an  ovate  body 
lodged  between  the  posterior  parts  of  the  cerebral  hemi- 
spheres. The  front  part  of  the  floor  of  the  ventricle,  on  the 
other  hand,  is  produced  into  a  bilobed  process  directed 
backwards,  which  is  the  infundibulum.  This  is  connected 
below  with  the  pituitary  body.  In  front  of  this  is  seen  the 
commissure  of  the  optic  nerves. 

Anteriorly,  the  third  ventricle  is  bounded  by  the  thick 
lamina  terminalis  which  contains  the  anterior  commissure. 
On  each  side,  between  this  and  the  peduncle  of  the  pineal 
gland,  is  a  small  aperture,  the  foramen  of  Munro,  which 
leads  into  a  cavity  in  the  interior  of  the  cerebral  hemisphere 
— the  lateral  ventricle. 

The  hemispheres  are  elongated  bodies,  broader  behind 
than  in  front,  where  they  are  marked  off  only  by  a  slight 


XIII.] 


THE  FROG. 


187 


constriction  from  the  olfactory  lobes.  The  outer  wall  of 
the  ventricle,  though  relatively  thick,  presents  nothing  which 
can  be  called  a  distinct  corpus  striatum.  The  inner  wall 
forms  one  or  two  convex  projections  into  the  ventricle. 

In  the  bases  of  the  olfactory  lobes  the  forward  continua- 
tion of  the  ventricular  cavity  is  very  narrow  and  the  lobes 
become  nerve-like  cords,  which  leave  the  skull  and  spread 
out  on  the  posterior  faces  of  the  olfactory  sacs. 

The  inner  faces  of  the  hemispheres  are  quite  free  and 
separated  by  a  cleft,  the  great  fissure,  but  the  inner  faces  of 
the  commencements  of  the  olfactory  lobes  are  closely  united 
together,  giving  rise  to  a  kind  of  corpus  callosum. 

There  are  ten  pairs  of  cranial  nerves  ordinarily  so  called, 
though  it  is  to  be  recollected  that  the  first  and  second  pairs 
are  proved,  by  their  development,  to  be  lobes  of  the  brain. 

1 .  O  I/actor ii. 

The  olfactory  lobes  are  what  answer  to  the  so-called 
olfactory  nerves  of  the  higher  Vertebrata.  They  are 
distributed  exclusively  to  the  olfactory  sacs. 

2.  Opt  id. 

These  diverge  from  the  base  of  the  brain  in  front  of 
the  infundibulum.  They  are  originally  outgrowths 
of  the  thalamencephalon  which  secondarily  become 
connected  with  the  optic  lobes. 

Of  the  remaining  cranial  nerves  five  pairs  leave  the  skull 
in  front  of  the  auditory  capsules,  while  one  pair  enters  those 
capsules  and  two  pairs  pass  out  behind  the  capsules. 

The  Prceauditory  nerves  are  the  following. 

3.  Mot  ores  oculorum 

arise  from  the  front  part  of  the  floor  of  the  mid-brain 
and  are  distributed  to  all  the  muscles  of  the  eye 


i88  ELEMENTARY  BIOLOGY.  [CHAP. 

except  the  external  rectus,  the  superior  oblique  and 
the  retractor  bulbi. 

4.  Pathetid 

arise  from  the  floor  of  the  mid-brain  and  pass  out, 
on  the  dorsal  aspect  of  the  brain,  between  the  cere- 
bellum and  the  optic  lobes.  They  are  distributed 
to  the  superior  oblique  muscles  of  the  eye. 

5.  Trigemini 

take  their  origin  in  the  front  part  of  the  floor  of  the 
hind-brain  and,  passing  out  at  its  sides,  each  dilates 
into  a  yellow  enlargement — the  Gasserian  ganglion — 
which  lies,  in  front  of  the  auditory  capsule,  in  the 
foramen  of  the  pro-otic  bone  by  which  the  nerve, 
after  leaving  the  ganglion,  passes  out  of  the  skull. 

This  ganglion  is  connected  with  the  trunk  of  the  sixth 
and  seventh  nerves  and  with  the  anterior  end  of  the  sym- 
pathetic, and  some  of  the  branches  which  appear  to  be 
given  off  from  it  really  belong  to  the  sixth  and  the  seventh 
nerves.  Beyond  the  ganglion,  the  nerve  divides  into  three 
main  branches,  the  orbito-nasal,  \hQ_palatine  and  the  maxillo- 
?nandibular. '  * 

i.     The  orbito-nasal  (usually  termed  the  first  division  of 
the  fifth  nerve)  is  distributed  : 

a.  To  the  external  rectus. 

b.  To  the  retractor  of  the  bulb. 

(These  branches  (a.  and  b.)  belong  to  the  sixth  nerve.) 

c.  A  branch  which  anastomoses  with  the  fourth 
nerve. 

d.  A  branch  to  the  Harderian  gland. 

e.  The  principal  trunk  of  the  nerve  passes  through 


xin.]  THE  FROG.  189 

the  ant-orbital  process  of  the  skull  into  the 
nasal  chamber  and  is  finally  distributed  to  the 
nasal  mucous  membrane  and  to  the  integu- 
ment of  the  nose. 

ii.     The  palatine  is  distributed  : 

a.  To  the  roof  of  the  oral  cavity. 

b.  Its  main  trunk  runs  forward  between  the  mucous 
membrane  of  the  roof  of  the  mouth  and  the 
skull,  pierces  the  vomer  and  ends  in  the  mucous 
membrane  of  the  anterior  part  of  the  palate. 

(This  nerve  is  chiefly,  if  not  wholly,  derived  from 
the  seventh  nerve.) 

iii.  The  maxillo-mandibular  divides  into  two  trunks, 
usually  termed  the  second  and  third  divisions  of  the 
fifth  nerve. 

a.  Maxillary,  passes  outside  the  eye  and  is  distri- 

buted to  the  integument  of  the  upper  jaw ;  an 
anastomotic  branch  unites  this  nerve  with  the 
palatine. 

b.  Mandibular,  passes  between  the  temporal  and 

pterygoid  muscles,  below  the  jugal,  over  the 
articulation  of  the  mandible  and  along  the  inner 
face  of"  the  latter,  to  the  symphysis,  giving  off 
branches  to  the  integument,  muscles,  teeth  and 
tongue. 

6.     Abducmtes 

arise  from  the  floor  of  the  hind-brain  and  leave  the 
ventral  surface  of  the  medulla  oblongata  close  to  the 
middle  line.  Each  then  unites  so  closely  with  the 
Gasserian  ganglion  and  with  the  orbito-nasal  division 


190  ELEMENTARY  BIOLOGY.  [CHAP. 

of  the  fifth  as  to  appear  to  be  only  a  subdivision  of 
the  latter  (see  5.  i.  a.  and  &). 

7.  The  Fadates 

take  their  origin  from  the  floor  of  the  hind-brain, 
behind  the  fifth  and  in  common  with  the  eighth; 
and,  leaving  the  hind-brain,  enter  into  close  con- 
nexion with  the  Gasserian  ganglion.  Each  then 
divides  into  two  branches,  an  anterior  and  a  pos- 
terior. The  anterior  passes  into  the  palatine  division 
of  the  fifth ;  the  posterior  passes  between  the  dorsal 
and  ventral  crura  of  the  suspensorium,  enters  the 
tympanic  cavity,  runs  over  the  columella  auris  and 
then,  as  it  leaves  the  tympanum,  receives  a  very 
large  branch  from  the  glossopharyngeal.  Finally  it 
divides  into  two  branches,  anterior  and  posterior. 

a.  The  former,  which  answers  to  the  chorda  tym- 
pani  of  the  higher  Vertebrata,  runs  along  the 
inner  face  of  the  ramus  of  the  mandible  parallel 
with  the  mandibular  branch  of  the  fifth. 

b.  The  posterior  passes  alongside  the  cornu  of  the 
hyoid  and  supplies  its  muscles. 

8.  The  Auditor  it 

arise  in  common  with  the  foregoing.  Each  divides 
into  two  branches  which  enter  the  auditory  capsule. 

The  Post-auditory  nerves  are : 

9.  The  Glossopharyngei. 

These  nerves  arise,  in  common  with  the  next,  from 
the  medulla  oblongata ;  and  the  roots  of  both  leave 
the  skull  by  an  aperture  behind  the  auditory  capsule 
on  each  side,  and  form  a  common  ganglion.  From 


xiii.]  THE  FROG.  191 

this  the  trunk  of  the  glossopharyngeal  is  given  off. 
It  passes  downwards  and  forwards  to  the  root  of  the 
tongue,  which  it  enters  and  then  supplies  that  organ. 
Moreover,  it  gives  off  muscular  branches  and  a  large 
anastomotic  branch  to  the  seventh. 

i  o.     The  Pneumogastrici  or  Vagi. 

Immediately  after  leaving  the  ganglia  these  nerves 
separate  from  the  glossopharyngeal  and  each  gives 
off  a  cutaneous  branch  to  the  dorsal  integument  of 
the  head  and  trunk :  it  then  divides  into  two 
branches,  one  of  which  (a.)  runs  on  the  inner  side  of 
and  above  the  cutaneous  branch  of  the  pulmo-cuta- 
neous  artery,  the  other  (£.)  lies  below  and  diverges 
from  the  first. 

a.  is  the  laryngeal  nerve.     It  passes  beneath   the 

first  cervical  nerve,  then  crosses  over  the  third 
aortic  arch  and,  about  its  middle,  turns  sharply 
round  it  to  be  distributed  to  the  larynx.  This 
nerve  corresponds  with  the  recurrent  laryngeal 
of  the  higher  animals. 

b.  is  the  splanchnic  branch.      It  gives  off  (gastric] 

branches  to  the  gullet  and  stomach,  and  a  fine 
nerve  (cardiac)  which  passes  beneath  the  pul- 
monary artery  and  along  the  root  of  the  lung  to 
the  heart,  and  ends  in  ganglia  situated  in  the 
septum  of  the  auricles.  The  splanchnic  branch 
finally  enlarges  and  is  distributed  to  the  lungs 
and  stomach. 

The  myeloii  or  spinal  cord  is  continued  back  from  the 
hind-brain  as  a  subcylindrical  cord,  which  lessens  somewhat 
rapidly  towards  its  apparent  end  at  the  level  of  the  seventh 
vertebra.  It  does  not  really  end  here,  however,  but  is  con- 


192  ELEMENTARY  BIOLOGY.  [CHAP. 

tinued  back  as  a  slender  filament,  t\\Qfilum  terminate,  to  the 
commencement  of  the  canal  of  the  urostyle.  The  diameter 
of  the  cord  is  somewhat  enlarged  opposite  the  origin  of  the 
nerves  for  the  limbs,  In  transverse  sections,  the  cord  is 
seen  to  be  not  truly  cylindrical  and  to  be  indented  by 
two  longitudinal  grooves,  one  dorsal  and  one  ventral,  which 
leave  but  a  small  connecting  bridge  between  its  two  halves. 
In  the  centre  of  this  is  a  canal,  the  canalis  centralis,  the 
Cavity  of  which  is  continued  forwards  into  the  fourth  ven- 
tricle. 

Ten  symmetrically  disposed  pairs  of  nerves  come  off 
from  the  sides  of  the  cord,  each  nerve  having  two  roots,  one 
from  the  dorsal  surface  of  the  lateral  half  of  the  cord  and 
one  from  the  ventral  half.  The  dorsal  root  presents  a 
small  ganglionic  enlargement,  beyond  which  it  joins  the 
ventral  root  to  form  the  common  trunk  of  the  spinal  nerve. 
The  roots  of  the  hinder  spinal  nerves  are  very  long  and  lie, 
side  by  side,  for  some  distance,  in  the  spinal  canal. 

The  first  spinal  nerve  leaves  the  neural  canal  by  the 
interspace  between  the  arches  of  the  first  and  second 
vertebrae,  so  that  there  is  no  suboccipital  nerve  in  the  Frog. 
It  gives  a  branch  to  the  muscles  which  move  the  head  upon 
the  atlas,  but  the  main  trunk  of  it  descends  behind  the 
mandible,  along  with  the  glossopharyngeal  nerve,  and  is 
distributed  to  the  muscles  of  the  tongue.  It  therefore 
answers  to  the  hypoglossal  nerve  in  the  higher  Vertebrata. 

The  second  and  third  spinal  nerves,  of  which  the  second 
is  the  larger,  unite  to  form  a  *  brachial plexus]  and  are  dis- 
tributed chiefly  to  the  fore-limb. 

The  fourth,  fifth  and  sixth  spinal  nerves  go  to  the  middle 
parietes  of  the  body. 

The  seventh,  eighth  and  ninth,  are  large  nerves  which 
unite  to  form  the  lumbosacral  plexus,  whence  nerves  are 


XIIL]  THE  FROG.  193 

given  off  to  the  posterior  parietes  of  the  body,  and  to  the 
hind-limb.  The  nerves  of  the  latter  are  the  crural  to  the 
front  part  of  the  thigh,  and  the  sciatic,  which  passes  to  the 
back  of  the  thigh  and  ultimately  divides  into  the  peronczal 
and  tibial  nerves  which  supply  the  leg  and  foot. 

The  tenth  spinal  nerve  leaves  the  neural  canal  by  the 
coccygeal  foramen,  and  is  distributed  to  the  adjacent 
parts. 

Sympathetic. 

The  sympathetic  system  consists  of  ten  ganglia,  connected 
by  longitudinal  commissures,  and  situated  on  each  side  of 
the  ventral  face  of  the  vertebral  column  ;  in  the  region  of 
the  dorsal  aorta  they  come  into  close  relation  with  it.  Each 
sympathetic  ganglion  is  joined  by  a  communicating  fila- 
ment with  one  of  the  spinal  nerves,  and  the  most  anterior 
ganglia  are  united,  in  the  same  way,  with  the  ganglion  of 
the  ninth  and  tenth  cerebral  nerves.  From  this  a  delicate 
cord,  which  must  be  regarded  as  the  most  anterior  part  of 
the  sympathetic,  passes  into  the  cranial  cavity,  on  the  inner 
side  of  the  periotic  capsule,  and  unites  with  the  Gasserian 
ganglion. 

The  branches  of  the  sympathetic  accompany  the  vessels, 
and  large  branches  are  given  to  the  viscera  of  the 
abdomen. 

The  Olfactory  organs  are  two  wide  sacs  which  occupy  all 
the  space  between  the  mesethmoid  cartilage,  the  antorbital 
processes,  and  the  premaxillae  and  maxillae,  and  open  in 
front  and  dorsally  by  the  external  nares,  behind  and  ven- 
trally  by  the  posterior  nares.  The  inner  faces  of  these  sacs 
are  lined  by  a  very  peculiar  epithelium,  and  the  olfactory 
nerves,  with  some  branches  of  the  trigeminal,  are  distributed 
to  them. 

M.  13 


I94  ELEMENTARY  BIOLOGY.  [CHAP. 

The  Eyeball  is  lodged  in  the  orbit  and  protected  by  the 
eyelids  described  above.  It  has  four  recti  muscles  which 
proceed  from  the  inner  wall  of  the  orbit,  and  are  attached 
to  the  circumference  of  the  globe  ;  within  these  is  a  retractor 
muscle  with  similar  attachments,  ensheathing  the  optic 
nerve,  while  two  oblique  muscles  proceed  from  the  anterior 
and  inner  wall  of  the  orbit  and  are  attached  to  the  dorsal 
and  ventral  faces  of  the  bulb.  In  addition,  a  fine  tendon 
passes  from  the  outer  end  of  the  lower  eyelid,  or  nictitating 
membrane,  and  is  attached  to  the  fibres  of  the  retractor 
bulbi  —  the  effect  of  which  is  that  when  the  bulb  is  retracted 
the  nictitating  membrane  is  raised  over  the  eye.  The  upper 
lid  has  no  muscles.  A  secretory  organ,  termed  the  Harde- 
rian  glandf  is  situated  in  the  anterior  part  of  the  orbit 
beneath  the  superior  oblique  rmiscle, 

The  sclerotic  is  cartilaginous  but  contains  no  ossifications, 
and  the  lens  is  nearly  spherical.  There  is 


The  Ear  consists  of  an  essential  part  —  the  membranous 
labyrinth  —  lodged  in  the  periotic  capsule,  and  accessory 
parts,  the  columella  auris,  the  tympanic  membrane  and  the 
tympanum. 

The  former  consists  of  the  three  ordinary  semicircular 
canals,  with  their  vestibular  dilatations,  which  open  into  a 
vestibule  divided  into  utriculus  and  sacculus.  The  latter, 
especially,  contains  a  great  quantity  of  white  crystalline 
calcareous  otol'iths. 

On  the  outer  side  of  the  vestibule  is  a  small  dilatation 
which  is  possibly  a  rudimentary  cochlea. 

The  membranous  labyrinth  is  contained  in  the  partly 
cartilaginous,  partly  osseous,  periotic  capsule  into  which  it 
fits  but  loosely;  the  interval  is  filled  with  a  fluid,  the  peri- 
lymph.  In  the  outer  face  of  the  periotic  capsule  is  an  oval 


xni.]  THE  FROG.  195 

opening,  the  fenestra  ovalis,  into  which  the  end  of  the 
columella  auris  fits.  This  columella  is  shaped  like  a  pestle, 
the  end  of  the  handle  of  which  is  fitted  with  a  cross-piece. 
The  rounded  inner  end  of  the  pestle,  which  is  fixed  by 
fibrous  tissue  into  the  fenestra  ovalis,  is  cartilaginous.  The 
middle  of  the  handle  is  ensheathed  in  bone,  while  the  outer 
part  is  cartilaginous.  The  cross-piece  is  fixed  into  the  inner 
face  of  the  membrana  tympani,  which  is  lined  externally  by 
the  integument,  internally  by  mucous  membrane,  continuous 
with  that  of  the  mouth  through  the  Eustachian  recess. 
The  mucous  membrane  of  the  tympanic  cavity  covers 
only  the  ventral  face  of  the  columella,  over  the  dorsal  face 
of  which  the  posterior  division  of  the  facial  nerve  passes. 

The  Tongue.  This  organ,  as  has  been  seen,  is  fixed  only 
in  front  to  the  mandible,  and  by  the  anterior  half  of  its  ven- 
tral aspect  to  the  floor  of  the  mouth;  the  posterior  half 
being  free  and  bifid  at  the  extremity.  Narrow-ended  and 
broad-ended  papillse  (papilla  filiformes  and  fungiformes)  are 
scattered  over  the  whole  dorsal  aspect  of  the  tongue  and  are 
largest  in  front ;  small  glands  lie  between  these  papillae. 

The  fungiform  papillae  contain  the  ultimate  ramifications 
of  the  glossopharyngeal  nerve,  and  the  epithelium  covering 
their  summits  is  peculiarly  modified. 

The  Integument.  No  special  organs  of  touch  have  been 
observed,  but  the  integument  is  remarkable  for  the  immense 
number  of  close-set  simple  glandular  caeca  which  open  upon 
its  surface.  In  the  swollen  integument  which  covers  the 
base  of  the  inner  digit  in  the  males,  large  papillae  with  inter- 
posed glands  are  developed. 

A  singular  body  of  unknown  function,  the  Irowspot  or 
inter-ocular  gland,  consisting  of  a  spheroidal  sac  with  minute 

13-2 


196  ELEMENTARY  BIOLOGY.  [CHAP. 

cells,  occurs  in  the  integument  of  the  frontal  region  of  the 
head. 

Cells  containing  pigment  abound  in  the  integument  and 
undergo  remarkable  changes  of  form,  the  pigment  being 
sometimes  drawn  together  into  a  spheroidal  mass — at  other 
times  distributed  in  a  radiating  fashion. 

LABORATORY  WORK. 
A.    GENERAL  STRUCTURE. 

1.  Go  over  the  specific  characters  given  above  (p,  164). 

2.  The  divisions  of  the  body:  head,  trunk,  two  pairs  of 
limbs  (see  p.  159). 

a.     The  head. 

Somewhat  triangular,  with  the  blunted  apex 
turned  forwards  and  passing  broadly,  without 
any  neck-constriction,  into  the  trunk;  notice 
the  prominent  eyes  with  their  lids ;  the  membrana 
tympani,  a  part  of  the  integument  stretched  over 
a  hard  ring,  placed  on  each  side,  behind  and 
somewhat  below  the  eyes ;  the  two  apertures  of 
the  nostrils  (anterior  nares)  between  the  eyes 
and  the  end  of  the  snout ;  the  mouth  opening; 
the  hard  parts  felt  through  the  skin  on  the 
upper  side  of  the  head ;  the  soft  flexible  throat. 

Pass  a  bristle  into  one  of  the  anterior  nares. 
Make  a  small  opening  in  one  of  the  tympanic 
membranes  and  pass  another  bristle  into  it 
Now  open  the  mouth  widely ;  and,  if  the  bristles 
have  been  thrust  far  enough,  the  end  of  the 
former  will  be  seen  traversing  the  posterior  nasal 
opening  in  the  roof  of  the  mouth  :  while  the  end 
of  the  other  will  appear  in  the  Eustachian  recess 


xiii.]  THE  FROG.  197 

which  lies  at  the  sides  of  the  back  of  the  oral 
cavity.  The  fleshy  tongue  will  be  seen,  with  its 
bifurcated  free  end  turned  backwards.  Turn  it 
forwards  to  see  the  attachment  of  its  base  to  the 
floor  of  the  mouth  and  to  the  front  part  of  the 
lower  jaw.  Notice  the  slit  of  the  glottis  in  the 
hinder  part  of  the  floor  of  the  mouth,  and  above 
this  the  opening  of  the  oesophagus.  Pass  a 
bristle  into  the  former,  and  a  probe  into  the 
latter.  Notice  the  fine  teeth  in  the  upper  jaw 
and  on  the  palate. 

b.  The  trunk. 

Tapering  towards  the  hinder  end  ;  and  allowing 
the  hard  parts  of  the  skeleton  to  be  felt  beneath 
the  soft  integument  on  the  dorsal  side,  and  in 
the  anterior  half  of  the  ventral  aspect ;  rounded 
and  soft  on  the  greater  part  of  the  sides  and 
belly;  the  cloacal  aperture  near  the  dorsal  surface 
of  the  posterior  end  of  the  trunk. 

c.  The  limbs. 

a.  The  anterior  pair;  their  three  subdivisions, 
brachium,  antebrachium,  and  manus;  the  four 
digits. 

/?.  The  posterior  pair ;  their  length  as  compared 
with  that  of  the  anterior;  their  subdivision 
into  femur,  crus,  and/£f :  the  five  long  digits ; 
the  well-developed  web  ;  the  horny  prominence 
(see  p.  161). 

3.  Raise  the  integument  of  the  abdomen  with  forceps 
and  slit  it  open  with  scissors  from  the  lower  jaw  to 
the  origin  of  the  hind  limbs,  a  little  on  one  side  of 
the  middle  line.  Observe  the  spacious  lymph  cavities 


r98  ELEMENTARY  BIOLOGY.  [CHAP. 

between  the  skin  and  the  subjacent  muscular  wall  of 
the  abdomen;  also  a  vein  which  occupies  the  middle 
line  of  the  inner  face  of  this  wall  and  is  usually 
visible  through  it. 

4.  Raise  the  muscular  wall  of  the  abdomen  and  cut  it 
in  the  same  way,  a  little  on  one  side  of  the  middle 
line;  sufficiently  to  lay  open  the  abdominal  cavity, 
taking  great  care  to  avoid  the  bladder  which  lies  at 
the   posterior   end   of  the   cavity.     Note   the   con- 
spicuous vein  [interior  abdominal)  which  lies  beneath 
the  muscles  in  the  middle  line  of  the  belly.     The 
liver,  stomach  and  intestines  will  be  seen;   at  the 
sides,  in  the  female,  the  ovaries  and  oviducts  will  be 
very  conspicuous  in  the  breeding  season.     Insert  a 
small  blow-pipe  into  the  cloacal  opening  :  air  blown 
in  will  distend  the  large  bilobed  urinary  bladder.     If 
the  lungs  are  distended  with  air,  one  will  be  visible 
on  each  side  of  the  anterior  end  of  the  abdominal 
cavity,  and  the  extremity  of  the  bristle  passed  into 
one  of  them,  through  the  glottis,  will  be  seen.     Lay 
open  the  stomach  to  see  the  end  of  the  probe  passed 
into  the  oesophagus. 

By  turning  the  intestines  on  one  side,  the  kidney,  the 
corpus  adiposum  and  the  testis  (in  the  male)  will  be 
exposed.  Notice  a  member  of  small  white  patches 
on  each  side  of  the  vertebral  column.  They  are 
accumulations  of  calcareous  crystals. 

5.  In  front  of  the  liver,  the  apex  of  the  heart  will  be 
seen  through  the  pericardium.     Lay  the  latter  open 
and  observe  the  position  of  the  heart. 

6.  Cut  away  the  left  fore-limb  and  the  left  hind-limb, 
with  so  much  of  the  left  half  of  the  vertebral  column 


XIIL]  THE  FROG.  199 

and  skull  as  is  needful  to  lay  open  the  cavity  which 
contains  the  cerebro-spinal  nervous  centres.  Pin 
the  frog  in  a  dissecting  dish,  on  its  right  side,  with 
sufficient  water  to  cover  it,  and  study  the  position  of 
the  various  organs  in  relation  to  a  median  longitu- 
dinal plane,  making  a  careful  diagram  of  the  parts 
displayed. 

7.  In  a  frog  which  has  lain  in  bone-softening  solution 
(say  i°/o  chromic  acid)  sufficiently  long  to  soften 
the  bones,  make  transverse  sections  (i)  through 
the  eyes,  (2)  through  the  centres  of  the  tympanic 
membranes,  (3)  through  the  shoulder-girdle,  (4) 
through  the  hinder  half  of  the  abdomen.  Compare 
them  with  the  foregoing  dissection. 

B.     DISSECTION  OF  THE  VISCERA  IN  THE  VENTRAL  CAVITY. 

i.  Lay  a  frog,  which  has  been  killed  with  chloroform, 
on  its  back  and  pin  it  out  on  a  layer  of  paraffin  or 
beeswax,  under  water;  divide  the  skin  along  the 
abdominal  median  line  from  the  pelvis  to  the 
front  of  the  lower  jaw;  next  make  a  transverse 
incision  at  each  end  of  the  longitudinal  one,  and 
then  throw  outwards  the  two  flaps  of  skin  thus 
marked  out.  The  following  points  may  now  be 
noted. 

a.  A  great  vein  (musculo-cutaneous]  on  the  under- 
surface  of  each  flap  of  skin,  about  the  level  of 
the  shoulder. 

b.  Some  of  the  muscles  of  the  abdominal  wall, 
covered  by  a  thin   aponeurosis:    through   this 
latter  can  be  seen — 

a.      The  rectus  abdominis  running  from  pelvis  to 


ELEMENTARY  BIOLOGY.  [CHAP. 

sternum  close  to  the  middle  line,  and  divided 
into  a  number  of  bellies  by  transverse  tendi- 
nous intersections. 

p.     Other  muscles   outside  the  rectus   on  each 
side. 

c.  The  pectoral  region  ;  part  of  its  hard  parts  in  the 
middle  line,  only  covered  by  tendinous  tissue: 
external  to  this,  muscles  running  towards  the 
shoulder-joint. 

d.  The  muscles  of  the  throat;   small   and  with  a 
general  direction   from  the  lower  jaw  towards 
the  sternum  and  shoulder-girdle. 

2.  Raise  the  tissues  of  the  body-wall  with  a  pair  of 
forceps  and  carefully  divide  them,  a  little  to  the 
right  of  the  median  line,  so  as  to  open  the  body- 
cavity  without  injuring  its  contents ;  prolong  the 
incision  from  the  pelvis  to  the  posterior  end  of  the 
breast-bone;  make  a  transverse  incision  close  to  the 
pelvis  and  throw  back  the  flap  on  each  side:  on  the 
deep  side  of  the  left  flap  will  be  seen  a  large  vein 
(anterior  abdominal]. 

Seize  the  posterior  border  of  the  sternum  with  a 
pair  of  forceps  and  raise  it  up :  on  looking  beneath 
it  several  fibrous  bands  will  be  seen  running  from  it 
and  the  hard  parts  in  front  of  it  to  subjacent  parts; 
carefully  divide  these:  then,  with  a  strong  pair  of 
scissors,  cut  through  the  hard  parts  in  the  median 
line,  being  very  careful  not  to  injure  the  organs 
beneath  them;  turn  each  half  outwards  and  pin  it  in 
that  position;  stretch  out  each  fore-limb  to  its  fullest 
extent  and  fasten  it  with  pins. 


xin.]  THE  FROG.  201 

3.  Note  the  smooth  moist  membrane  (pleuroperitoneuni) 
lining  the  inside  of  the  body-cavity  and  covering  the 
outside  of  the  contained  viscera. 

4.  The  liver  will   be   readily  recognized    as   a  great 
brownish  mass  covering  a  great  part  of  the  other 
abdominal  viscera:   lying  in  a  cleft  in  its   anterior 
border  and  partly  concealed  by  it,  will  be  seen  a 
delicate  sac  in  which  pulsations  are  going  on;  this 
sac  is  the  pericardium:  if  it  be  opened  and  removed 
very   carefully,    the  heart   and   some   of  the  great 
blood-vessels  will  be  laid  bare;  clean  carefully  the 
two  great  trunks  (aortic  arches)  which  diverge  from 
the  anterior  end  of  the  heart,  following  each  to  the 
point  of  its  division  into  three  vessels. 

5.  The  heart. 

a.     Note  the  general  form  of  the  organ. 

a.  Its  posterior  conical  thick-walled  portion  ^ven- 
tricle) with  the  apex  turned  backwards. 

b.  The  truncus  arteriosus:  a  sub-cylindrical  part, 
arising  from  the  right  side  of  the  base  of  the 
ventricle  and  dividing  anteriorly  into  the  two 
aortic  arches. 

c.  The  atrium:  thin-walled,  rounded,  lies  on  the 
dorsal  aspect  of  the  truncus  and  ventricle.    The 
separation  between  the  two  auricles  is  not  visi- 
ble externally. 

d.  Carefully  raise  the  ventricle:   lying  beneath  it 
(that  is,  on  its  dorsal  side)  will  be  seen  another 
division  of  the  heart,  the  sinus  venosus ;  it  lies 
between  the   atrium    and   the  great    systemic 


202  ELEMENTARY  BIOLOGY.  [CHAP. 

veins,   which  enter  it  through  the  dorsal  and 
posterior  walls  of  the  pericardium. 

e.  The  further  examination  of  the  structure  of  the 
Frog's  heart  requires  a  good  deal  of  care  and 
the  use  of  a  lens  of  low  magnifying  power.  In 
a  chloroformed  Frog  the  heart  is  distended 
with  blood  when  it  ceases  to  beat.  When  all 
signs  of  contractility  have  disappeared,  the  dis- 
tended heart  should  be  removed  from  the  body 
by  cutting  through  the  adjacent  parts  in  such  a 
manner  as  to  leave  the  terminations  of  the 
veins  and  the  origins  of  the  aortic  trunks 
intact.  The  organ  should  next  be  transferred 
to  a  shallow  dissecting  dish  and  covered  with 
weak  spirit.  The  right  and  left  walls  of  the 
atrium  being  now  carefully  slit  and  the  blood 
which  they  contain  washed  away,  the  delicate 
septum  of  the  auricles  will  become  visible.  By 
cautiously  removing  the  ventral  face  of  the 
ventricle,  its  cavity  will  be  laid  open  and  the 
auriculo-ventricular  opening  will  be  displayed. 
If  the  ventral  wall  of  the  truncus  arteriosus  is 
laid  open  longitudinally  with  fine  scissors,  the 
valves  in  its  interior  will  become  visible.  The 
pulmonary  vein  runs  along  the  dorsal  aspect  of 
the  sinus  venosus,  between  the  right  and  left 
superior  venae  cavse,  to  the  left  auricle,  into 
which  it  opens  close  to  the  dorsal  attachment 
of  the  septum. 

The  natural  relations  of  the  different  divi- 
sions of  the  heart  should  be  carefully  studied  in 
such  a  dissection  as  is  described  in  A.  6. 


XIIL ]  THE  FROG.  203 

b.  The  pulsation  of  the  heart.  This  should  be  stu- 
died in  a  Frog  rendered  insensible  by  chloroform 
or  by  being  pithed;  though  the  latter  operation 
causes  such  dilatation  of  the  vessels  that  little  or 
no  blood  may  afterwards  flow  through  the  heart, 
yet  the  organ  goes  on  beating. 

a.  Watch  the  movement  carefully;  it  is  a  regu- 
larly alternating  series  of  contractions  and  dila- 
tations. 

b.  It  will  be  seen  that  the  two  auricles  contract 
together;  immediately  after  them,  the  ventricle; 
and  then,  instantly,  the  bulbus  arteriosus. 

c.  Raise  the  ventricle  so  as   to   see  the  venous 
sinus;  note  that  it  contracts  immediately  before 
the  auricles. 

6.      The  parts   exposed  by  the   preceding  dissections 

(B.  i.  2). 

Draw  them  carefully  without  disturbing  them. 

a.  The  throat-muscles:  through  the  broad  thin  mus- 
cle in  front  (mylo-hypid)  is  seen  the  hypoglossal 
nerve. 

b.  The  larynx:  forming  a  hard  prominence  in  the 
middle  line,  just  in  front  of  the  aortic  arches. 

c.  The  heart  and  aortic  arches  (see  B.  5.  i.) :   the 
three  terminal  branches  of  the  latter,  viz. — 

a.      The  carotid  trunk;  the  anterior  division;  end- 
in  a  small  reddish  body  (the  carotid  gland). 

p.      The  systemic  aortic  arch, 
y.      The  pulmo-cutaneous    artery:    the   hindmost 
branch. 


104  ELEMENTARY  BIOLOGY.  [CHAP. 

d.  The  liver:  a  great  brown  two-lobed  mass;  its 
left  lobe  the  larger  and  subdivided  into  two. 

c.  The  lungs:  the  posterior  ends  of  these  may  be 
seen  as  sacculated  pouches,  one  on  each  side  of 
the  liver,  but  they  are  frequently  not  visible 
until  the  latter  organ  has  been  removed. 

f.  The  stomach:  a  small  portion  of  this  is  seen  pro- 
jecting beyond  the  lower  left  border  of  the 
liver. 

g.  The  intestine:  a  convoluted  tube,  continuous  with 
the  stomach,  and  slung  by  a  delicate  membrane, 
the  mesentery:  posteriorly  the  intestine  ends  in  a 
dilated    portion   (rectum)   which  runs  into  the 
pelvis. 

h.  The  urinary  bladder:  a  thin-walled  bilobed  sac 
(which  may  or  may  not  be  distended)  appear- 
ing just  in  front  of  the  pelvis. 

/.  The  fat  masses:  long  slender  yellow  processes 
appearing  on  each  side  of  the  liver. 

In  R.  temporaria,  the  urinary  bladder  is  much 
more  deeply  lobed  and  also  much  larger  propor- 
tionately, than  in  R.  esculenta, 

7.     The  liver. 

a.  Study  its  form  more  closely.     (6.  d.)     ,v 

b.  Raise  its  lower  border;  between  its  two  lobes 
will  be  seen  a  small  greenish  sac,  the  gall-bladder. 

c.  Carefully  cut  away  the  liver,  except  its  deepest 
part,  close  to  the  venous  sinus. 

d.  Tease  out.  a  bit  of  liver  in  07  5 £  sodic  chloride 
solution  and  examine  with  -J  obj. 


xiii.]  THE  FROG.  205 

a.  Numbers  of  polygonal  granular  cells  (hepatic 
cells],  with  oil-drops  in  them,  will  be  seen. 

/?.  Treat  with  acetic  acid :  a  nucleus,  or  sometimes 
two,  will  be  rendered  apparent  in  each  of  the 
cells. 

8.     The  stomach,  intestine,  pancreas  and  spleen. 

a.      Cut  away  the  front  of  the  pelvis  with  a  stout 
pair  of  scissors,  taking  care  not  to   injure  the 
urinary  bladder:   pass  a   probe  from  the  anus, 
through  the  cloaca,  into  the  rectum:  uncoil  the 
intestine  and  spread  out  the  mesentery,  so  far  as 
is  possible  without  cutting  the  latter. 
a.      The  spleen:   a   small   red   body  lying  in  the 
mesentery,  near  its  attachment  to  the  back  of 
the  abdomen. 

/3.      The   stomach:   an  elongated  sac  on  the  left 
side  of  the  abdominal  cavity:  the  narrower 
tube  (oesophagus)  opening  into  its  anterior  end. 
y.      The  intestine:   its  length  and  varying  diame- 
ter; especially  the  great  width  of  its  rectal 
portion :  its  posterior  termination  in  the  cloaca. 
3.      The  pancreas:  a  pale-coloured  compact  mass 
lying  in  the  mesentery  near  the  commence- 
ment of  the  intestine. 

e.  The  bile-duct.  Slit  open  the  duodenum  where 
the  right  end  of  the  pancreas  is  attached  to 
it:  a  small  aperture  will  be  seen  on  the 
mucous  membrane  of  the  intestine  at  this 
point:  this  is  the  opening  of  the  bile-duct: 
pass  a  bristle  into  it. 
£.  The  mesentery:  its  width;  mode  of  attach- 


?o6  ELEMENTARY  BIOLOGY.  [CHAP. 

ment  to  the  intestine;  the  blood-vessels  run- 
ing  in  it. 

b.  Divide  the  oesophagus  close  to  the  stomach  and 
the  rectum  near  the  cloaca :  remove  all  the  por- 
tion of  alimentary  canal  between  these  two 
points,  cutting  through  the  mesentery. 

a.      Pass  a  probe  up  the  oesophagus  into  the  mouth. 

/?.  Open  the  upper  end  of  the  intestine  and  snip 
off  a  bit  of  its  internal  layer  (mucous  mem- 
brane) and  mount  in  normal  saline  solution: 
examine  with  -J  obj.;  on  the  fragment  will  be 
found  minute  prominences  (representing  the 
villi  of  the  higher  animals)  covered  by  a  closely- 
Set  layer  of  cells  (epithelium}. 

9.  The  kidneys.  These  organs  afe  now  exposed  as  two 
elongated  deep  red  bodies  lying  itt  the  posterior 
part  of  the  perivisceral  space  close  to  the  verte- 
bral column ;  clear  away  any  bits  of  mesentery,  &c. 
which  may  cover  them;-  note — 

a.  The  duct — ureter  (female)  or  gemto-urinary  canal 
(male) — running  from  the  outer  side  of  the  pos- 
tsrior  part  of  each  kidney  to  the  cloaca.    Open 
the  cloaca  and  pass  a  bristle  into  the  opening  of 
one  of  the  ureters. 

b.  In  the  male  R.  esculenta  each  duct  is  somewhat 
dilated  after  leaving  the  kidney :  it  then  narrows 
again  and  opens  on  the  posterior  surface  of  the 
cloaca  by  an  oblique  slit  with  sharply  denned 
edges.     In  R.  temporaria   the   duct   does   not 
dilate,  or  only  very  slightly;  but  on  its  outer 
side  lies  a  glandular  mass  (vcsicula  seminalis), 


xiii.]  THE  FROG.  207 

from  the  inner  side  of  which  a  number  of  minute 
ducts  open  into  the  genito-urinary  canal.  The 
aperture  of  the  -latter  in  the  cloaca  is  round 
and  has  tumid  edges.  In  the  female  of  both 
species  the  ureters  are  very  slender. 

c.  The  vein  (renal  portat]  entering  the  kidney  at 
its  posterior  outer  border. 

d.  The  great  vein  (vena  cava  inferior]  lying  between 
the  kidneys  arid  chiefly  formed  by  their  efferent 
(renal)  veins. 

Now  that  the  cloaca  is  open,  trace  the  open- 
ing of  the  urinary  bladder  (B.  6.  h)  into  it. 

10.     The  generative  organs. 
a.      In  the  male. 

a.  The  testes:  a  pair  of  yellowish  bodies  lying 
in  front  of  the  ariterior  ends  of  the  kidneys; 
their  form. 

(3.  The  ducts  of  each  testicle  (vasa  efferentid] 
entering  the  inner  border  of  the  kidney  of  the 
same  side  in  order  to  communicate  with  the 
genito-urinary  canal  (9.  a). 

y.  Remove  the  testes :  open  one  and  press  out 
some  of  its  contents  upon  a  slide  and  mount 
in  common  water:  examine  with  |-  objective. 

The  spermatozoa:  bodies  provided  with  a 
small  oval  head  and  a  long  vibratile  tail  in  7?. 
esculenta:  in  R.  temporaria  the  oval  head  is 
absent :  their  movements. 

b.     In  the  female. 

a.      The  ovary :    an  organ  varying  much  in  size 


2o8  ELEMENTARY  BIOLOGY.  [CHAP. 

with  the  season  of  the  year.     The  numerous 
ova  in  it. 

ft.  The  oviduct:  a  convoluted  tube,  not  con- 
tinuous with  the  ovary,  and  running  back  to 
open  into  the  cloaca.  The  greater  part  of 
the  oviduct  is  opaque  and  glandular;  the 
part  near  the  cloaca  however  is  dilated,  thin- 
walled  and  transparent.  The  oviducts  open 
on  the  posterior  wall  of  the  cloaca  a  little 
anterior  to  the  openings  of  the  ureters. 

ii.     The  mouth,  oesophagus,  and  respiratory  organs. 

a.  Open  the  mouth :  note  on  its  roof  near  the  front 
the  two  hinder  openings  of  the  nasal  cavities 
(posterior  nares);   farther  back,  the  two  larger 
openings  of  the  Eustachian  recesses ;    the  long 
tongue  in  the  floor  of  the  mouth;  fixed  by  its 
front  end  to  the  lower  jaw;  its  free  bifid  end 
turned  towards  the  throat. 

b.  Enlarge  the  mouth-opening  by  cutting  through 
the  sides  of  the  buccal  cavity  with  a  pair  of 
scissors :  pull  down  the  lower  jaw  so  as  to  see 
the  chamber  (pharynx)  behind  the  mouth. 

c.  On  the  floor  of  the  pharynx  is  a  narrow  opening 
(the  glottis) :  pass  a  probe  down  it  through  the 
larynx  and  very  short  trachea  into  the  lungs. 

d.  Remove  the  lungs ;  open  one ;  it  is  a  thin-walled 
cavity  with  a  sacculated  inner  surface. 

e.  Trace  the  oesophagus  up  to  the  pharynx. 

C.       THE  CIRCULATION  OF  THE  BLOOD  IN  THE  FROG'S  WEB. 

i.     Get   a  piece  of  thin  board,    about   5    inches   long 
and  2\  broad ;  in  the  middle  of  one  end  of  it  cut 


xiii.]  THE  FROG.  209 

a  V-shaped  notch  about  the  size  of  a  spread-out 
frog's  web  :  place  the  frog  on  the  board,  belly  down- 
wards, and  fix  it  by  passing  round  it  two  or  three 
turns  of  tape  :  next  tie  threads  round  the  toes  of  one 
hind-foot,  and  by  means  of  them  spread  out  the  web 
over  the  notch  in  the  board,  taking  great  care  that  it 
is  only  very  lightly  stretched.  The  animal  should  be 
kept  moist  by  a  bit  of  wet  blotting-paper  spread  over 
its  back. 

2.      Examine  the  web  with  i  inch  obj.  :  Note — 

a.  The  black  pigment-cells  in  the  skin ;  sometimes 
irregularly  branched ;  sometimes  more  compact. 

b.  The  close  network  of  blood-vessels  lying  deeper 
than  the  pigment-cell  layer. 

a.  The  arteries,  running  mainly  towards  the  free 
edge  of  the  web,  and  constantly  diminishing 
in  size  as  they  give  off  branches ;  the  blood- 
flow  in  them  from  larger  to  smaller  branches. 

J3.  The  capillaries,  in  which  the  arterial  branches 
end :  small  vessels  forming  a  close  network 
and  frequently  branching  or  anastomosing 
without  much  altering  their  size. 

y.  The  veins,  formed  by  the  ultimate  union  of 
the  capillaries,  and  increasing  in  size  by  union 
with  one  another;  the  blood-flow  in  them 
from  smaller  to  larger  trunks. 

c.  The  blood-flow:   the  current  being  marked  by 
the  solid  bodies  (corpuscles)  carried  along  in  the 
fluid  :  it  is  most  rapid  in  the  arteries ;  slowest, 
and  most  uniform,  in  the  capillaries. 

M.  14 


ELEMENTARY  BIOLOGY.  [CHAP. 

Place  a  small  drop  of  water  on  a  bit  of  a  thin  cover- 
glass,  and  place  the  bit,  with  the  water  downwards, 
gently  on  the  web :  then  examine  the  following  points 
with  \  or  \  obj. ;  note — 

a.  The  'walls  of  arteries ,  capillaries,  and  veins. 

a.      The  arterial  walls,  tolerably  thick,  seen  as  a 

clear  well-defined  band  on  each  side  of  the 

blood-stream. 
p.      The  capillary  walls ;  difficult  to  see ;  merely 

a  thin  somewhat  more  transparent  boundary 

line. 

y.     The  venous  walls ;  much  like  the  arterial. 

b.  The  blood-flow  in  the  small  arteries  of  the  web. 

a.      The  rapid  stream  in  the  middle,  containing 

most  of  the  red  corpuscles. 
ft.     The    slower    stream    along  the   edge   (inert 

layer),  containing  many  colourless  corpuscles. 

c.  The  flow  in  the  capillaries :  much  slower  than  in 
the  arteries ;  the  frequent  distortion  of  the  red 
corpuscles  in  the  capillaries  from  pressure,  &c. ; 
their  elasticity  as  indicated  by  the  readiness  with 
which  they  recover  their  shape  when  the  cause 
of  distortion  is  removed;    the   way  the   white 
corpuscles  creep  along,  with  a  tendency  to  stick 
to  the  capillary  wall. 

Examine  a  drop  of  frog's  blood  with  the  microscope 
(J-or-|  obj.).  Sufficient  blood  to  supply  a  whole  class 
for  this  purpose  can  be  obtained  by  killing  one  frog 
and  opening  its  heart. 

It  consists  of  solid  bodies  (corpuscles)  floating  in 
fluid  (plasma). 


XIIL]  THE  FROG.  211 

a.  The  red  corpuscles. 

a.  Their  form :  oval  when  seen  in  front  face ; 
almost  linear  in  profile  but  slightly  swollen  at 
the  centre. 

/?.  Their  size:  their  length,  breadth,  and  thick- 
ness; measure. 

y.  Their  colour :  pale  yellow,  when  seen  indivi- 
dually; redder  if  a  thick  mass  of  them  is 
looked  at. 

8.  Their  structure:  they  are  homogeneous  for 
the  most  part,  but  possess  a  round  granular 
central  nucleus. 

€.  Treat  with  water ;  they  swell  up  and  become 
more  spherical ;  their  colouring  matter  is  gra- 
dually discharged;  the  nucleus  is  rendered 
very  evident,  and  ultimately  all  the  rest  of  the 
corpuscle  disappears. 

£.  Treat  with  dilute  acetic  acid;  results  same 
as  with  water,  but  produced  more  rapidly. 

b.  The  white  corpuscles. 

Less  numerous  than  the  red :  their  colour,  size, 
granular  character,  nucleus,  and  changes  of  form 
(amoeboid  movements] :  see  III.  B. 

D.       THE    EXAMINATION    OF   A   PREPARED    SKELETON. 

The  skeleton  of  a  Frog  may  be  prepared  for  ex- 
amination by  removing  the  viscera  from  the  body, 
and  roughly  dissecting  away  the  muscles,  &c.  Then 
place  the  remainder  in  water  and  let  it  macerate 
for  about  a  week;  afterwards  carefully  pick  away 
the  soft  parts,  with  forceps,  from  the  bones  and  carti- 
lages. 

14—2 


2  ELEMENTARY  BIOLOGY.  [CHAP. 

a.  Its  general  arrangement. 

1.  The  central  axis,  consisting  of  the  vertebral  or  spinal 
column  and  of  the  central  parts  of  the  skull  which 
lie,  in  front  of  the  spinal  column,  in  the  same  antero- 
posterior  line. 

2.  Lateral  parts,  supported,  directly  or  indirectly,  by 
the  axis. 

a.  The  appendages  proper.   (Limits  and  limb-arches.} 
a .     The  fore-limbs :  their  supporting  shoulder-girdle 

or  pectoral  arch,  not  directly  attached  to  the 
axial  column;  the  limb  proper;  its  main  di- 
visions; humerus,  radius  and  ulna  (the  two 
latter  ankylosed),  carpus  and  digits. 
/?.  The  hind-limbs :  their  supporting  arch  (pelvic 
girdle),  carried  directly  by  bony  processes 
proceeding  from  the  vertebral  column;  the 
limb  proper ;  its  main  divisions,  os  femoris, 
tibia  and  fibula  (ankylosed),  tarsus,  digits. 

b.  The  facial  and  lateral  cranial  bones. 

b.  The  vertebral  column. 

It  consists  of  an  anterior  segmented  portion  (each 
segment  being  a  vertebra)  and  of  a  posterior  un- 
segmented  portion  (the  urostyle). 

i.     Examine  carefully  and  draw  various  aspects  of  a  de- 
tached vertebra,  say  the  third. 

a.  Its  solid  flattened  ventral  part   centrum)',  with 
an   anterior  concave  and  a  posterior  convex 
surface. 

b.  The  neural  arch:  an  arch  of  bone  springing 
from  the  sides  of  the  dorsal  aspect  of  the  cen- 


xiii.]  THE  FROG.  213 

trum  of  the  vertebra  and  not  quite  so  wide  as 
the  centrum  in  its  antero-posterior  diameter. 

a.  The  transverse  process :  a  bony  bar  on  each 
side,  arising  from  the  arch  and  passing  out- 
wards and  a  little  downwards. 

(3.  The  articular  processes  (zygapophyses);  an  an- 
terior and  posterior  pair,  springing  from  the 
sides  of  the  arch ;  the  anterior,  having  their 
smooth  articular  surfaces  directed  upwards ; 
the  posterior  with  similar  surfaces  directed 
downwards.. 

y.  The  short  spinous  process,  springing  from  the 
dorsal  aspect  of  the  arch  and  directed  back- 
wards. 

c.      The  neural  canal  enclosed  between  the  arch  and 
the  body. 

2.      Examine  the  remaining  vertebrae. 

a.  The  first  vertebra   (atlas):   its   body  produced 
forwards  into  a  wedge-shaped  process  which  lies 
between  the  occipital  condyles :  its  arch,  some- 
times incompletely  ossified  in  the  region  "of  the 
spinous  process,  which  is  rudimentary;  posterior 
zygapophyses  only  present:  the  large  concave 
anterior  facets,  partly  on  the  arch  and  partly  on 
the  centrum,  with  which  the  skull  articulates. 

b.  The  2nd,  4th,  $th,  6th  and  7th  vertebrae  :  closely 
resembling  the  third,  the  chief  differences  being 
found  in  the  varying  size  and  direction  of  the 
transverse  processes,  all  of  which  are  smaller 
than  those  of  the  third  vertebra. 


2 14  ELEMENTAR Y  BIOLOGY.  [CHAP. 

c.  The  8th  vertebra:  the  concave  facet  at  each  end 
of  its  centrum. 

d.  The  Qth  vertebra  (sacrum) :  its  centrum;  convex 
in  front  and  with  two  convex  tubercles  behind  : 
its  large  strong  transverse  processes  (sacral  ribs] 
directed  somewhat  backwards  and  expanded  at 
their  ends. 

3.  The  posterior  unsegmented  portion  of  the  vertebral 
column  (urostyle}. 

a.  An  elongated  rod-like  bone,  rather  thicker  to- 
wards its  anterior  end,  which  bears  two  con- 
cavities. 

b.  Its  posterior  end  j  tubular  in  the  dried  skeleton, 
but  in  the  fresh   state  filled  with   a  cartilage 
which  projects  beyond  it  posteriorly. 

c.  The  prominent  ridge  along  its  dorsal  surface; 
wider  and  higher  in  front ;  getting  thinner  and 
gradually  disappearing  towards  the  posterior  end. 

d.  The  small  canal  contained  in  the  forepart  of 
the  ridge. 

e.  The  two  minute  passages  leading  from  the  canal 
to  the  outside  of  the  ridge  on  each  side. 

4.  The  vertebral  column  as  a  whole. 
a.     Its  composition. 

a.      Its  anterior  segmented  part  formed  of  the  nine 

vertebrae. 
P.     Its  posterior  unsegmented  part  formed  by  the 

urostyle  and  nearly  as  long  as  the  segmented 

part. 


xiii.]  THE  FROG.  215 

b.  Its  ventral  surface. 

a.  The  solid  bony  axis  formed  by  the  bodies 
of  the  vertebrae  in  front  and  continued  pos- 
teriorly by  the  ventral  rounded  part  of  the 
urostyle. 

/3.  The  transverse  processes :  their  size  and  direc- 
tion :  those  of  the  second  vertebra,  slender 
and  directed  nearly  straight  outwards;  those 
of  the  third  and  fourth,  largest  of  all  and  with 
a  distinct  inclination  backwards  :  those  of 
the  fifth,  sixth,  seventh  and  eighth  vertebrae 
smaller  than  the  rest  and  directed  nearly  out- 
wards ;  those  of  the  ninth,  very  stout,  directed 
outwards  upwards  and  backwards,  and  having 
the  iliac  bones  attached  to  their  distal  ends. 
The  transverse  processes  arise  from  their 
arches  closer  to  the  centrum  in  the  second, 
third  and  fourth  vertebrae  than  in  the  others. 

y.  The  inter-vertebral  foramina :  the  interspaces 
left  between  each  pair  of  neural  arches,  below 
the  level  of  the  zygapophyses. 

c.  The  dorsal  surface  of  the  spinal  column. 

a.  The  ridge  down  its  middle  formed  by  the  row 
of  spinous  processes,  and  continued  behind 
by  the  dorsal  ridge  of  the  urostyle. 

P.  The  lateral  prominences  caused  by  the  ar- 
ticular processes :  the  articulations  between 
the  anterior  articular  processes  of  one  verte- 
bra, and  the  corresponding  posterior  processes 
of  its  predecessor. 

y.     The  spaces  left  between  the  dorsal  part  of 


116  ELEMENTARY  BIOLOGY.  [CHAP. 

each  neural  arch  and  its  successor  :  between 
the  atlas  and  the  second  vertebra  and  be- 
tween the  eighth  and  ninth  vertebrae ;  these 
are  almost  obliterated  by  the  approach  of  the 
respective  arches. 

d.     The  neural  canal. 

a.  Closed  by  the  centra  of  the  vertebrae  beneath, 
and  incompletely  by  the  neural  arches  on  the 
sides  and  above :  its  backward  continuation 
as  the  canal  in  the  front  part  of  the  ridge  of 
the  urostyle. 

/3.  The  communication  with  it,  of  the  inter- 
vertebral  foramina  (4.  b.  y),  and  the  dorsal 
intervals  between  the  neural  arches  (4.  c.  y) : 
also  of  the  openings  in  the  urostyle  (3.  e). 

c.  The  skull.  The  prepared  bony  skull  of  the  frog 
is  difficult  to  understand,  for  two  reasons ; 
firstly,  on  account  of  the  dried-up  condition  of 
the  cartilages  of  which,  in  the  fresh  state,  it  is  in 
part  composed ;  and,  secondly,  on  account  of 
the  tendency  of  many  of  its  constituent  bones 
to  become  ankylosed  together  in  the  adult :  the 
following  points  can  however  be  made  out  with 
tolerable  ease.  Drawings  should  be  made  of 
each  aspect  of  the  skull. 

i .     Examine  the  posterior  end  of  the  skull. 

a.  The   large   aperture  (foramen  magnum}  in  the 
middle  line,  leading  into  the  cranial  cavity. 

b.  The  convex  surface  (occipital  condyle),  on  each 
side  of  the  foramen  magnum,  which  articulates 


XIII.]  THE  FROG.  >  217 

with  the  corresponding  concave  facet  on   the 
front  of  the  atlas. 

c.  The  bone  bearing  the   condyle  on  each  side 
and,  with  its  fellow,  enclosing  the  foramen  mag- 
num, is  the  exoccipital. 

d.  The  thick  bone  running  outwards  in  front  of 
the  exoccipital,  on  each  side,  protects  the  front 
part  of  the  internal  ear,  and  is  fatprwtic  bone. 

e.  Between  these  two  bones,  on  the  outer  side  of 
the  chamber  which  contains  the  organ  of  hear- 
ing (periotic  capsule),  is  a  cartilaginous  inter- 
space containing  an  oval  aperture,  $\efenestra 
walls.    In  this  is  fixed  the  inner  end  of  a  partly 
cartilaginous  and  partly  osseous  rod,  the  colu- 
metta  aurls. 

f.  Attached  to  the  outer  end  of  the  pro-otic  bone 
is  a  hammer-shaped  bone — the  sqttamosal,  which 
extends  from  the  pro-otic  bone  to  the  articu- 
lation of  the  lower  jaw. 

2.     The  roof  of  the  skull. 

a.  Passing  forwards  from  the  exoccipitals  are  two 
long  flat  bones,  the  parleto-frontals,  one  on  each 
side  of  a  median  suture  which  answers  to  the 
sagittal  and  frontal  sutures  in  man. 

b.  In  front  of  these  come  two  triangular  bones— 
the  nasals. 

c.  In  front  of  the  nasals  are  two  other  bones,  which 
belong  rather  to  the  ventral  than  to  the  dorsal 
face  of  the  skull.     They  form  the  extreme  front 
of  the  snout,  and  each  sends  a  process  towards 
the  nasals;  these  are  the premaxlllary  bones. 


8  ELEMENTARY  BIOLOGY.  [CHAP. 

3 .     The  base  of  the  skull. 

a.  Running  along  the  greater  part  of  the  floor  of 
the   cranial  cavity,  from  the  occipital  foramen 
•to  the  vomers,  is  a  bone  shaped  like  a  dagger 
with  a  short  handle  and  a  strong  guard.    The 
latter  spreads  out  under  the  pro-otics.     This  is 
the  parasphenoid  bone. 

b.  Appearing  at  the  base  of  the  skull,  at  the  front 
end  of  tf  c  parasphenoid,  is  the  girdle-bone  or 
sphenethmoid  (which    represents   several  bones 
joined  together);  this  bone  closes  in  the  floor 
>and  sides  of  the  forepart  of  the  cranial  cavity  and 
also  its  roof,  being  concealed  in  the  latter  place 
by  the  anterior  ends  of  the  parieto-frontals.    The 
sphenethmoid  has  a  single  cavity  behind,  which 
enters  into  the  formation  of  the  cephalic  chamber, 
and  two   cavities  in  front,  one  for  each  nasal 
chamber,  separated  by  a  septum. 

c.  Running  out  transversely  from  the  girdle-bone 
and  the  anterior  end  of  the  blade  of  the  para- 
sphenoid  on  each  side,  is  the  slender  palatine. 

d.  In  front  of  the  end  of  the  blade  of  the  para- 
sphenoid  and  of  the  palatines  are  two  broad 
irregularly  shaped  bones,  each  bearing  an  oblique 
row  of  teeth  on  its  posterior  part :  these  are  the 
vomers. 

e.  The  middle  anterior  boundary  of  the  contour  of 
the  skull,  in  this  view,  is  formed  by  the  denti- 
gerous   parts  of  the  pre-maxillse ;  and,  behind 
them,  by  the  maxillae   and  the  quadrato-jugal 
bones  (4.  a.  b).     Running  backwards  from  the 


xiii.]  THE  FROG.  219 

outer  end  of  the  palatine,  and  closely  applied  to 
the  maxilla,  is  a  bone,  which  soon  separates 
from  the  maxilla,  and  becoming  broad  and 
stout,  bifurcates;  the  inner  process  nearly  joins 
the  parasphenoid  and  is  moveably  articulated 
with  the  skull;  the  outer  runs  along  the  inner 
face  of  a  cartilage  (the  $uspensorium\  on  the 
outer  face  of  which  the  squamosal  rests :  this  is 
the  pterygoid  bone. 

At  the  outer  edge  of  each  vomer,  immediately 
in  front  of  the  palatine,  is  an  aperture  which 
leads  into  the  nasal  cavity.  These  two  apertures 
are  the  posterior  nares. 

4.      The  side  of  the  skull. 

a.  Running  back  from  that  part  of  the  pre-maxilla 
which  bounds  the  gape  is  a  long  bone,  forming 
almost  the  whole  of  the  rest  of  the  upper  edge 
of  the  gape;  this  is  the  maxilla. 

b.  Joined  to  the  posterior  end  of  the  maxilla  is  a 
small  bone,  which  at  its  posterior  end  is  attached 
to  the  distal  portion  of  the  squamosal.     This  is 
the  quadrato-jugal. 

c.  The  under  jaw  or  mandible  consists  of  two  dis- 
tinct portions,  or  rami,  which  meet  in  the  middle 
line  in  front,  and  which,  behind,  articulate  with 
the   extremities   of  the  suspensorial  cartilages. 
In  the  articular  end  of  each  suspensorial  cartilage 
there  is   an  ossification   which  represents  the 
quadrate  bone  in  other  Vertebrata,  and  is  united 
with  the  jugal  to  form  the  quadrato-jugal. 

In  each  ramus  three  pieces  may  be  made  out — 


ELEMENTAR  Y  BIOL OG  Y.  [CHAP. 

a.  A  central  axis  formed  of  cartilage  (MeckeFs 
cartilage),  which  enlarges  at  its  posterior  end 
in  order  to  articulate  with  the  suspensorial 
cartilage,  while  at  the  opposite  or  symphysial 
end  it  is  ossified  to  form  the  mento-Meckdian 
bone. 

(3.  A  posterior  inferior  piece,  which  runs  nearly  to 
the  middle  line  in  front  (angulo-splenial]  and 
partly  ensheaths  the  foregoing. 

y.      A  small  anterior  superior  piece  (dentary). 

d.  The  hyoid  bone  or  cartilage. 

a.  Its  broad  somewhat  tetragonal  central  part 
(body),  bearing  a  number  of  processes,  viz. — 

/?.  The  anterior  corntta,  proceeding  from  the 
front  of  the  body  on  each  side :  each  is  a 
long  slender  curved  cartilage  running  at  first 
forwards,  then  backwards  and  outwards,  and 
finally  forwards  and  upwards,  to  become  at- 
tached to  the  periotic  capsule  beneath  the 
fenestra  ovalis. 

y.  The  posterior  cornua,  or  thyro-hyals ;  bony, 
and  shorter  and  thicker  than  the  anterior 
cornua:  attached  to  the  posterior  border  of 
the  body  near  the  middle  line  and  diverging 
as  they  run  backwards. 

3.  Two  pairs  of  smaller  processes  formed  by  the 
elongation  of  the  anterior  and  posterior  an- 
gles of  the  body  of  the  hyoid. 

e.  The  sternum  and  shoulder-girdle. 

i.     Their  general  arrangement:  they  form  an  incomplete 
ring  round  the  fore-part  of  the  trunk :   this  ring  is 


UNIVERSITY 


\m.]  THE  FROG. 

composed  partly  of  bone,  partly  of  cartilage.  Note 
the  hollow  (glenoid  fossa)  with  which  the  fore-limb 
articulates. 

a.  The  sternum  :  situate  in  the  ventral  median  line 
and  made  up  of  several  parts  :  beginning  behind 
we  find  — 

a.  The  xiphisternum  ;  a  thin  cartilage,  wide 
behind,  narrow  in  front,  where  it  passes 
into— 

p.  A  median  cartilage  ensheathed  in  bone,  the 
sternum  proper.  The  anterior  end  of  the 
sternum  unites  with  the  posterior  and  inter- 
nal angles  of  the  coracoids  (b.  y),  the  inner 
edges  of  which  meeting  in  the  middle  line 
separate  the  sternum  from  — 

y.  The  omosternum,  consisting  of  a  slender,  flat- 
tened bone,  terminated  in  front  by  an  ex- 
panded cartilage.  The  posterior  end  arti- 
culates with  the  praecoracoids  and  the  clavi- 
cles. 

b.  The  shoulder-girdle:  beginning  dorsally,  it  ex- 
hibits on  each  side  — 

a.  A  thin  expanded  dorsal  portion,  partly  car- 
tilaginous, partly  ossified  :  the  supra-scapula. 

P.  Next  a  bony  segment  —  the  scapula,  the  pos- 
terior inferior  edge  of  which  is  excavated  by 
the  glenoidal  fossa. 

The  ventral  parts  of  the  shoulder-girdle,  which 
lie  between  the  two  scapulae,  meet  in  the  mid- 
dle line;  the  part  on  each  side  is  subdivided 


222  ELEMENTARY  BIOLOGY.  [CHAP. 

into  an  anterior  and  a  posterior  portion  by  a 
large  foramen. 

y.  The  bony  piece  running  behind  the  foramen, 
from  the  scapula  almost  to  the  middle  line, 
is  the  coracoid.  Where  the  coracoid  unites 
with  the  scapula  it  contributes  to  the  forma- 
tion of  the  glenoidal  cavity. 

8.  The  adjacent  margins  of  the  two  coracoids 
are  fringed  with  cartilage  (epicoracoid\  which 
passes  in  front  of  the  foramen  into  a  bar  of 
cartilage — the  prczcoracoid — which,  externally, 
is  continuous  with  the  cartilage  which  lies 
tween  the  scapula  and  coracoid  and  helps  to 
bound  the  glenoidal  cavity. 

e.  Closely  attached  to  the  fore-part  of  the  prae- 
coracoid  lies  a  bone,  the  clavicle,  the  outer 
end  of  which  articulates  with  the  coracoid 
and  scapula,  the  inner  with  the  omosternum. 

Draw   the   whole   pectoral   arch   carefully,    shading 
differently  the  bones  and  cartilages. 

f.    The  bones  of  the  fore-limb. 

a.      The  arm-bone  (humerus). 

a.  A  somewhat  cylindrical  bone,  with  an  arti- 
cular expansion  at  each  end  and  a  shaft  unit- 
ing them. 

p.  The  great  ridge  (deltoid  crest)  on  its  antero- 
internal  surface,  to  which  a  muscle  was  at- 
tached. 

The  development  of  this  crest  is  greater  in 
the  males  than  in  the  females.  - 


XIIL]  THE  FROG.  223 

b.  The  bone  of  the  forearm. 

a.  Hollowed  out  above  to  fit  the  lower  end  of 
the  humerus. 

/?.  Shewing  below  a  tendency  to  divide  into  the 
two  bones  of  which  it  is  made  up;  viz.  the 
radius  and  the  ulna.  When  the  limb  is 
stretched  out  at  right  angles  to  the  body 
with  the  pollex  forwards,  the  radius  is  on  the 
anterior,  and  the  ulna  on  the  posterior  side 
of  the  axis  of  the  limb. 

c.  The  carpus.     Two  bones  (a,  b)  articulate  with 
the  ankylosed  radius  and  ulna.     A  third  bone 
(c\  on  the  radial  side  of  the  carpus,  articulates 
only  with  the  carpal  bones  on  the  proximal  and 
distal  sides  of  it.     A  large  bone  (d)   occupies 
two-thirds  of  the  ulnar  side  of  the  carpus,  and 
articulates  with  a,  b  and  c  on  one  side,  and 
with  the  third,  fourth  and  fifth  metacarpals  on 
the  other.     Two  small  ossicles  articulate  with 
the  distal  face  of  c  and  bear  the  first  and  second 
metacarpals. 

d.  The  digits. 

Five  in  number,  the  first  (radial  one)  being, 
however,  rudimentary:  beginning  at  the  ulnar 
side,  we  find — 

a.  The  fifth  digit  (that  on  the  outer  or  ulnar 
side  of  the  limb) :  it  presents  a  cylindrical 
proximal  bone  (metacarpal]  followed  by  three 
others  (phalanges\  each  shorter  than  its  pre- 
decessor. 

p.  The  fourth  digit :  a  metacarpal  bone  and  three 
phalanges. 


224  ELEMENTARY  BIOLOGY.  [CHAP. 

y.      The  third  digit:  a  metacarpal  bone  with  two 

phalanges. 
8.     The  second  digit :  a  metacarpal  bone  with  two 

phalanges.    /. .  . ' 
c.      The   first  digit   (pollex)   consists   only  of    a 

small  metacarpal  bone. 

g.    The  pelvic  girdle. 

a.  Its  general  form :    V-shaped,    with   the    apex 
turned  backwards. 

b.  The  concavity  (acetabulum)  on  each  side  with 
which  the  thigh-bone  articulates. 

c.  The  triradiate  fissure  running  through  the  aceta- 
bulum and  dividing  each  half  of  the  pelvis  into 
three  pieces,  viz. — 

a.  An  anterior  elongated  piece  (ilium)  •  subcy- 
lindrical  in  front,  where  it  articulates  with 
the  sacrum ;  bearing  behind,  on  its  dorsal 
aspect,  a  laterally  compressed  ridge  of  bone 
(crista  ilii)',  it  forms  almost  half  of  the  aceta- 
bulum. 

/?.  A  posterior,  irregularly  rounded  piece  (is- 
chium)-,  closely  united  posteriorly  with  its 
fellow,  in  the  middle  line. 

y.  A  small  triangular  piece  (os  pubis),  (calcified 
cartilage — except  in  old  frogs),  wedged  in 
between  ilium  and  ischium,  and  meeting  its 
fellow  in  the  median  ventral  line,  thus  form- 
ing the  symphy sis  pubis. 

h.    The  bones  of  the  lower  limb 

a.  The  thigh-bone  (os  femoris);  its  long  cylindrical 
shaft  and  expanded  articular  extremities. 

b.  The  leg-bone  (os  cruris). 


XIIL]  THE  FROG. 


225 


a.  A  very  long  cylindrical  bone,  expanded  at 
each  end. 

/?.  The  grooves  on  it;  one  running  along  the 
whole  ventral  surface,  but  most  marked  near 
the  ends;  other  grooves  on  the  dorsal  sur- 
face, one  at  the  upper,  another  at  the  lower 
extremity:  these  indicate  that  the  os  cruris 
is  really  made  up  of  two  united  bones,  the 
fibula  and  the  tibia.  When  the  limb  is 
stretched  out  at  right  angles  to  the  body,  the 
tibia  is  anterior,  corresponding  with  the 
radius;  and  the  fibula,  posterior,  correspond- 
ing with  the  ulna. 

c.  The  tarsus. 

a.  Two  elongated  bones  (separate  in  the  middle 
but  united  by  confluence  of  their  cartilagin- 
ous extremities)  articulate  with  the  ankylosed 
tibia  and  fibula;  the  anterior,  or  tibial,  of 
these  is  the  astragalus;  the  posterior,  or 
fibular,  the  calcaneum. 

fi.  With  the  distal  ends  of  these,  two  partially 
ossified  cartilages,  one  on  the  calcaneal  and 
the  other  on  the  astragalar  side,  articulate. 
The  latter  is  connected  by  ligamentous 
fibres,  within  which  a  nodule  of  cartilage 
may  be  found,  with  the  first  and  second  meta- 
tarsals,  and  supports  the  calcar  (d.  £). 

d.  The  digits.     Five  in  number;  the  internal  one 
the  shortest,  the  fourth  the  longest.    Their  com- 
position— 

a.  The  first,  or  hallux  (the  most  internal) ;  a 
metatarsal  bone,  followed  by  two  phalanges. 

M.  15 


226  ELEMENTARY  BIOLOGY.  [CHAP. 

j3.      The  second:  same  as  a,  but  longer. 

y.  The  third :  a  metatarsal  bone  with  three  pha- 
langes. 

8.      The    fourth :    a  metatarsal    bone    and   four 

phalanges. 
c.      The  fifth :  like  the  third,  but  a  little  shorter. 

£.  On  the  anterior  or  tibial  edge  of  the  foot  there 
are  two,  small,  more  or  less  cartilaginous, 
ossicles,  articulated  with  the  tarsus  (c.  (3)  in 
such  a  manner  as  to  resemble  an  extra  digit 
This  calcar,  or  spur,  supports  the  horny  pro- 
minence referred  to  above. 

E.     DISSECTION  OF  THE  FROG'S  HIND-LIMB  TO  ILLUSTRATE 

ITS   MYOLOGY. 

(For  the  following  dissection  it  is  desirable  to  have  a 
frog  which  has  been  lying  some  time  in  spirit.) 

1.  Lay  the  animal  on  its  back,  and  make  an  incision 
through  the  skin  on  the  front  of  the  limb  from  the 
symphysis  pubis  to  the  ankle ;  then  reflect  the  skin 
to  each  side  so  as  to  lay  bare  the  parts  beneath  it; 
in  turning  it  back  note  the  loose  bands  and  fibres 
(subcutaneous  areolar  tissue]  with  large  lymph-spaces 
between   them,  which  unite  the  skin  to  subjacent 
parts,  and  which  have  to  be  cut  through. 

A  number  of  muscles  will  now  be  exposed  on  the 
front  of  the  thigh  and  leg. 

2.  The  superficial  muscles  on  the  front  of  the  thigh. 
Separate   these    gently  from    one    another,   tearing 
through  the  connective  tissue  which  unites  them. 


xin.]  THE  FROG.  227 

a.  Each  is  chiefly  made  up  of  a  mass,  the  belly 
of  the  muscle,  which  is  nearly  white  and  readily 
tears  into  bundles  in  a  muscle  which  has  been  in 
spirit;    but  is  softer,  redder,  and  does  not  so 
easily  split  up  in  a  fresh  muscle. 

b.  At  both  ends,  in  most  cases,  the  belly  is  replaced 
by  dense  shiny  tissue  forming  a  tendon. 

c.  The  tendons  are  fixed  directly  or  indirectly  to 
some  of  the  neighbouring  bones,  the  less  move- 
able  attachment  being  the  origin  of  the  muscles ; 
the  point  of  attachment  to  the  more  moveable 
bone,  its  insertion. 

d.  The  names  of  the  muscles  laid  bare  on  the  front 
of  the  thigh,  are — 

a.  The  sartorius:  a  thin  flat  riband-like  muscle 
running  down  the  middle ;  it  arises  from  the 
symphysis  pubis  and  is  inserted  into  a  tendi- 
nous expansion  (aponeurosis)  on  the  inner  side 
of  the  knee-joint. 

/?.  The  adductor  magnus:  it  becomes  superficial 
along  the  upper  two-thirds  of  the  inner  border 
of  the  sartorius. 

y.  The  adductor  brevis:  a  little  bit  of  it  is  seen 
on  the  inner  side  of  the  adductor  magnus, 
close  to  the  symphysis  pubis. 

8.  The  rectus  interims  major:  a  large  muscle 
running  along  the  whole  inner  side  of  the 
thigh;  arises  from  the  symphysis  pubis  below 
the  sartorius  and  is  inserted  into  the  same 
aponeurosis  as  that  muscle. 

e.      The  rectus  internus  minor:  a  thin  muscle  lying 


228  ELEMENTARY  BIOLOGY.  [CHAK 

inside  and  rather  behind  the  rectus  internus 
major.  It  arises  from  the  pelvis  close  to  the 
anus  and  is  inserted  into  the  aponeurosis  about 
the  knee-joint. 

&  The  adductor  longus:  it  is  partly  superficial 
along  the  outer  edge  of  the  sartorius. 

17.  The  vastus  internus:  a  very  large  muscle  on 
the  outer  anterior  aspect  of  the  thigh;  arising 
from  the  pelvis  close  to  the  hip-joint,  it  joins, 
below,  two  muscles  on  the  back  of  the  thigh 
(4.  a.  (3.  y),  and  all  end  in  a  tendon  which  is 
inserted  into  the  aponeurosis  over  the  front  of 
the  os  cruris. 

e.  Cut  across  the  belly  of  the  sartorius,  and  turn  its 
ends  out  of  the  way ;  dissect  out  the  origin  and 
insertion  of  the  adductor  longus  and  the  adductor 
magnus  (d.  £.  and  ft). 

a.  The  adductor  longus  arises  from  the  anterior 
inferior  part  of  the  syiliphysis  of  the  iliac 
bones ;  by  its  lower  end  it  joins  the  adductor 
magnus. 

ft.  The  adductor  magnus  arises  from  the  pelvis, 
between  the  origin  of  the  sartorius  and  that 
of  the  rectus  internus  major.  Its  fibres  are 
inserted  directly  (i.e.  without  the  intervention 
of  a  specialised  tendon)  into  the  inner  side  of 
the  distal  half  of  the  femur. 

3.      The  deep  muscles  on  the  front  of  the  thigh. 

a.  Divide  and  reflect  the  adductor  Icngus,  rectus 
internus  major  and  rectus  internus  minor.  The 
following  muscles  will  be  displayed : — 


XIII.] 


THE  FROG. 


229 


a.  The  pectineus:  it  lies  at  the  upper  part  of  the 
thigh  immediately  internal  to  the  vastus  inter- 
nus:  it  arises  from  the  front  of  the  pelvis, 
close  to  the  symphysis,  and  is  inserted  into 
the  anterior  surface  of  the  distal  half  of  the 
femur. 

/?.  The  adductor  brevis  (2.  d.  y) :  it  lies  along  the 
inner  side  of  the  pectineus  and  arises  and 
is  inserted  close  to  it. 

y.  The  semitendinosus :  this  is  a  long  slender 
muscle  lying  beneath  the  rectus  internus  major 
and  bifurcated  at  its  upper  end :  its  two  heads, 
thus  formed,  arise,  one  (anterior  head]  from 
the  pelvis  between  the  ischial  symphysis  and 
the  acetabulum;  the  other  (posterior  head} 
from  the  ischial  symphysis :  the  muscle  termi- 
nates below  in  a  rounded  tendon  which  is 
inserted  along  with  the  sartorius. 

4.      Turn  the  frog  over  on  to  its  belly,  and  remove  the 
skin  from  the  back  of  the  limb. 

The  muscles  on  the  back  of  the  thigh.    These  are : — 

a.  The  triceps  femoris :  a  very  large  muscle  on  the 
outer  side,  divided  above  into  three  heads,  which 
are  often  regarded  as  separate  muscles,  viz. 

a.  The  vastus  internus:  the  anterior  division, 
which  has  been  already  seen  on  the  front  of 
the  thigh.  (2.  d.  17.) 

/?.  The  vastus  externus :  the  posterior  division  ; 
it  arises  from  the  hinder  edge  of  the  iliac 
bone. 


230  ELEMENTARY  BIOLOGY.  [CHAP. 

y.  The  rectus  femoris  anticus :  the  middle  divi- 
sion of  the  triceps ;  it  arises  from  the  pos- 
terior part  of  the  ventral  border  of  the  iliac 
bone.  For  the  insertion  of  the  triceps  femo- 
ris, see  2.  d.  rj. 

b.  The  glutaus :  this  muscle  arises  from  the  hinder 
two-thirds  of  the  external  surface  of  the  ilium ; 
it  runs  down  between  the  vastus  externus  and 
the  rectus  anticus  to  be  inserted  into  the  back 
of  the  head  of  the  femur. 

c.  The  pyriformis.      This  arises  from  the  posterior 
part   of  the   urostyle   and,   passing  inside  the 
vastus  externus,  is  inserted  into  the  shaft  of  the 
femur. 

d.  The  biceps  femoris :   a  long  thin  muscle,  lying 
along  the  inner  side  of  the  vastus  externus ;  it 
arises  from  the  iliac  bone  above  the  acetabulum ; 
below  it  divides  into  two  pieces,  one  of  which 
is  inserted  into  the  middle  of  the  shaft  of  the 
femur,  while  the  other  ends  in  a  rounded  tendon 
which  is  inserted  into  the  back  of  the  distal  end 
of  the  same  bone. 

f.  The  semimembranosus :  a  large  muscle  inside  the 
biceps ;  it  arises  from  the  upper  posterior  part 
of  the  iliac  symphysis  and  is  inserted  into  the 
aponeurosis  round  the  knee-joint. 

Lying  deep  in  the  thigh,  between  the  biceps 
and  semimembranosus  muscles,  will  be  seen  the 
femoral  vessels  and  the  sciatic  nerve. 

f.  Divide  and  reflect  the  vastus  externus  and  the 
biceps :  beneath  them  will  be  laid  bare — 


xni.]  THE  FROG.  231 

The  ileo-psoas :  it  arises  from  the  internal 
surface  of  the  posterior  part  of  the  ilium  and  is 
inserted  into  the  posterior  aspect  of  the  shaft  of 
the  femur. 

g.  Remove  the  pyriformis,  cut  through  the  semi- 
membranosus  close  to  its  origin  and  throw  it 
downwards ;  this  brings  into  view  a  small  tri- 
angular muscle — 

The  quadratus  femoris,  which  arises  from  the 
ilium  behind  the  acef  abulum  and  is  inserted  into 
the  middle  of  the  shaft  of  the  ventral  surface  of 
the  femur. 

h.  The  obturatorius :  this  is  a  small  muscle  lying 
on  the  dorsal  surface  of  the  hip-joint. 

5.     The  muscles  of  the  leg. 

a.  Turn  the  frog  on  its  back,  and  remove  the  skin 
from  the  foot :  fix  the  dorsal  surface  of  the  foot 
upwards.  The  os  cruris  will  now  be  seen  run- 
ning down  the  middle  of  the  leg.  Lying  on  its 
present  inner  (proper  dorsal)  side  are  two  mus- 
cles, viz. — 

a.  The  gastrocnemius :  a  muscle  with  a  great 
fleshy  belly ;  it  arises  above  by  two  tendons ; 
one  (much  the  larger)  is  inserted  behind  the 
knee-joint  partly  into  the  femur,  partly  into 
the  os  cruris ;  the  other  joins  the  aponeurosis 
on  the  outer  side  of  the  knee-joint.  Be- 
low, the  muscle  ends  in  a  great  tendon  (tendo 
Achittis),  which  terminates  in  an  aponeurosis 
on  the  plantar  surface  of  the  foot 


232  ELEMENTARY  BIOLOGY.  [CHAP. 

P.  The  tibialis  posticus :  a  slender  muscle  co- 
vered in  great  part  by  the  gastrocnemius ;  it 
arises  from  the  greater  part  of  the  posterior 
surface  of  the  os  cruris  and,  passing  along  the 
inner  side  of  the  ankle-joint,  is  inserted  into 
the  astragalus. 

b.      On  the  opposite  side  of  the  bone  lie  four  mus- 
cles :  viz. — 

a.  The peroneus:  the  largest  and  most  external; 
it  arises  from  the  outer  side  of  the  distal  arti- 
cular end  of  the  femur  and,  running  past  the 
outer  side  of  the  ankle-joint,  is  inserted  into 
the  calcaneum. 

P.  The  tibialis  anticus :  a  small  muscle  inside 
and  beneath  the  peroneus ;  it  arises  from  the 
front  of  the  lower  end  of  the  femur  and  from 
the  capsule  of  the  knee-joint;  below  it  di- 
vides into  two  parts,  one  inserted  into  the 
dorsal  side  of  the  astragalus,  the  other  into 
the  calcaneum. 

y.  The  extensor  cruris  brevis  :  this  lies  internal  to 
the  upper  part  of  the  last  muscle;  it  arises 
from  the  front  of  the  distal  articular  end  of 
the  femur  and  is  inserted  into  the  middle  third 
of  the  os  cruris. 

8.  The  flexor  tarsi  anterior :  this  arises  where 
the  last  muscle  ends,  and  is  inserted  into  the 
dorsal  side  of  the  astragalus. 

6.     The  nerves  of  the  hind-limb. 

These  are  now  to  be  dissected  out  in  that  leg  which 
has  not  been  used  for  the  muscles. 


XIIL]  THE  FROG.  233 

a.  The  sciatic  nerve. 

o.  Find  it  on  the  dorsal  side  of  the  thigh  by 
separating  the  biceps  and  semimembranosus 
muscles  j  it  appears  as  a  slender  white  cord. 

P.  Dissect  it  out  carefully  in  the  middle  of  the 
thigh,  noting  the  branches  it  gives  off  to  the 
various  muscles. 

y.  Follow  it  up  to  the  abdominal  cavity,  cutting 
away  the  tissues  lying  between  the  ilium  and 
urostyle,  which  cover  it  in. 

8.  Follow  it  down  towards  the  knee  :  a  little 
way  above  the  joint  it  divides  into  two 
branches;  one  (posterior  tibiat)  runs  inside 
the  large  head  of  the  gastrocnemius  muscle, 
the  other  (peroneal)  between  its  two  heads. 

b.  The  posterior  tibial  nerve. 

a.  Note  especially  the  branch  which  it  gives  off 
opposite  the  Imee-joint,  and  which,  after  run- 
ning for  some  way  along  the  deep  surface  of 
the  gastrocnemius,  enters  that  muscle. 

ft.  Follow  the  nerve  down  the  leg  :  it  runs  along 
the  tibialis  posticus  muscle,  giving  off  branches 
here  and  there. 

y.  Near  the  foot  it  turns  to  the  back  of  the 
ankle-joint  and  enters  the  plantar  surface 
of  the  foot,  where  it  ends  in  a  number  of 
branches. 

c.  TJie  peroneal  nerve. 

a.  This  runs  down  the  leg  close  to  the  peroneus 
muscle,  giving  off  branches  on  its  way. 


234  ELEMENTARY  BIOLOGY.  [CHAP. 

/3.  Towards  the  bottom  of  the  leg  it  comes  to 
the  front  of  the  ankle-joint,  and  divides  into 
branches  which  are  distributed  on  the  dorsum 
of  the  foot. 


[F.    DISSECTION  OF  THE  VASCULAR  SYSTEM. 

The  dissection  of  the  blood-vessels  is  much  facilitated  by 
previous  injection:  this  maybe  done  as  follows:  Dissolve 
some  gelatine,  with  the  aid  of  heat,  in  a  coloured  fluid 
(solution  of  carmine  or  of  Berlin  blue) ;  the  gelatine  ought 
to  be  added  in  such  quantity  that  the  fluid  just  sets  when 
cold :  kill  a  frog  with  chloroform ;  lay  bare  its  heart,  taking 
care  not  to  injure  the  anterior  abdominal  vein ;  prick  a 
small  hole  in  the  venous  sinus  and  sop  up  any  blood  that 
flows  out;  pass  a  ligature  round  the  trunctts  arteriosus; 
make  a  small  aperture  in  the  ventricle  and  pass  a  glass 
tube,  drawn  out  to  a  fine  point,  through  the  ventricle  into 
the  arterial  bulb,  and  tie  it  in ;  fill  this  tube  with  normal 
salt  solution  and  connect  it,  by  a  bit  of  gutta  percha  tubing, 
with  a  syringe  filled  with  the  injecting  fluid,  which  should 
not  be  warmer  than  35°  C. ;  inject  very  slowly  and  with 
slight  pressure.  The  venous  system  may  also  be  readily 
injected  by  dividing  the  anterior  abdominal  vein  and 
passing  the  syringe  into  its  posterior  end.  When  the  in- 
jection is  finished,  put  the  animal  in  alcohol  for  some 
hours.]  .  ; 

i.      The  anterior  abdominal  vein. 

a.  Carefully  dissect  the  belly-walls  away  from  the 
anterior  abdominal  vein :  at  its  posterior  end 
this  vessel  will  be  found  to  get  a  small  branch 
from  the  front  of  each  thigh  and  then  to  divide 
into  two  large  trunks  (pelvic  veins)  which  nin, 
,  .  c  one  on  each  side,  towards  the  back  of  the  thigh. 


XIII.]  THE  FROG.  235 

b.  Turn  the  animal  over  and  follow  one  of  these 
trunks  back  :  it  will  be  found  to  be  continuous 
with  the  sciatic  vein,  which  ends  in  the  pelvis 
by  dividing  into  this  and  another  (renal  portai) 
vessel. 

c.  Trace  the  anterior  abdominal  vein  forwards :  it 
divides  into  two  branches,  one  of  which  goes  to 
the  right  and  the  other  to  the  left  lobe  of  the 
liver. 

2.  Raise  the  liver,  and  note  the  vena  portse  which  enters 
its  lower  surface;  it  is  formed  by  the  union  of  a  vein 
(gastric)  from  the  stomach  with  one  (lieno-intestinal) 
from  the  spleen  and  intestines.  The  gastric  division 
of  the  vena  portae  communicates  by  a  large  branch 
with  the  left  division  of  the  anterior  abdominal  vein. 

3-      The  veins  of  the  head  and  neck  and  fore-limbs. 

a.  Remove  the  liver,  being  careful  not  to  injure 
the  inferior  vena  cava  beneath  it. 

b.  Pass  a  bit  of  glass  tube  down  the  frog's  gullet 
(in  order  to  stretch  out  the  neighbouring  parts) 
and  clean  the  aortic  arches :  passing  in  front 
of  each  aortic  arch,  near  its  point  of  division  is — 

c.  The  external  jugular  vein,  running  up  the  side  of 
the  throat  towards  the  angle  of  the  lower  jaw 
and  receiving  the  veins  of  the  mandibular  and 
lingual  regions. 

d.  Follow  this  vein  down  towards   the  heart :  a 
little  way  below  the  aortic  arch  it  is  joined  by 
another  large  vein — 

e.  The  subdavian:   follow   this  outwards;   it  will 
be  found  to  be  formed  mainly  by  the  union 


ELEMENTARY  BIOLOGY.  [CHAP. 

of  two  large  branches  :  one  (axillary  or  brachial 
vein]  coming  from  the  antebrachium  and  manus ; 
the  other  (inusculo-cutaneous)  from  the  back  and 
head. 

f.  The  innominate  vein  is  formed  by  the  union  of 
the  internal  jugular  vein,  which  brings  back  the 
blood  from  the  brain  and  spinal  cord,  with  the 
subscapular  vein  returning  the  blood  from  the 
brachium  and  shoulder. 

g.  The  superior  vena  cava   (right  and   left):   this 
is  formed  by  the  union  of  the  subclavian,  ex- 
ternal jugular  and  innominate  veins  on  each 
side :  follow  it  to  the  heart,  where  it  ends  by 
entering  the  sinus  venosus. 

The  inferior  vena  cava  and  renal  portal  veins. 

a.  Divide  the  alimentary  canal  above  the  stomach 
and  also  close  to  the  cloaca,  and  remove  the 
intermediate  portion  :  dissect  out  the  veins  con- 
nected with  the  kidneys. 

b.  The  renal  portal  vein:  running  from  the  bifur- 
cation of  the  pelvic  vein  to  enter  the  lower- 
outer  border  of  the  kidney. 

c.  The   inferior  vena  cava:   the  large  vein  lying 
between    the    kidneys  and  chiefly  formed   of 
branches  from  them,  but  also  getting  branches 
from  the  generative  organs  and  the  liver. 

d.  Follow  it  up  to  its  anterior  ending  in  the  sinus 
venosus. 

The  aortic  arches  and  their  "branches. 
a.      Dissect  out  the  branches  of  the  aortic  arches: 
three  on  each  side. 


XIIL]  THE  FROG.  237 

a.  The  anterior  division  (carotid  trunk} :  it,  after 
giving  off  a  branch  (lingual  artery)  which  runs 
up  the  throat,  ends  in  a  small  red  body,  the 
carotid  gland,  from  which  other  arteries  pro- 
ceed. 

/?,  The  systemic  aortic  arch:  this  is  the  middle 
and  largest  division  :  it  runs  round  the  throat 
towards  the  vertebral  column,  giving  off  on 
its  way  the  subclavian  artery  which  runs  to 
the  fore-limb. 

y.  The  pulmo-cutaneous  artery,  or  posterior  di- 
vision of  the  aortic  arch :  it  runs  to  the  root 
of  the  lung,  giving  off  on  its  way  a  cutaneous 
branch  which  runs  out  to  the  integument 
about  the  shoulder. 

b.  Imbed  in  paraffin  an  aortic  arch  which  has  been 
hardened  in  spirit  and  cut  transverse  sections 
of  it :  examine  with  i  inch  obj.  Note  the  two 
partitions  subdividing  it  into  three  channels. 

6.    The  dorsal  aorta  and  its  branches. 

a.  Remove  the  kidneys  with  vena  cava  inferior  and 
the  generative  organs :   the  dorsal  aorta  is  then 
laid  bare  lying  on  the  bodies  of  the  vertebrae. 

b.  Follow  the  systemic  aorta  (5,  a,  /?)  round  the 
neck;  they  will  be  found  to  unite  beneath  the 
vertebral  column  to  form  the  dorsal  aorta. 

c.  Follow  the  aorta  backwards:  it  gives  off  many 
branches  on  its  course;  note  the  large  one  (cce- 
liaco-mesenteric  artery}  arising  from  it  just  below 
its  point  of  formation. 


238  ELEMENTARY  BIOLOGY.  [CHAP. 

d.  Small   branches   to   the   renal    and   generative 
organs  (only  the  cut  ends  of  these  branches  can 
now  be  found)  and  to  the  muscles  of  the  back. 

e.  Near  the  pelvis .  it  ends  by  dividing  into  two 
trunks  (the  iliac  arteries]  which  run  behind  the 
pelvic  bones,  giving  off  hypogastric  branches  to 
the  bladder  and  the  walls  of  the  abdomen. 

f.  Turn  the  animal  over  on  to  its  belly  and  trace 
the  iliac  arteries  backwards:  they  are  mainly 
continued  down  the  thigh  as  the  femoral  arte- 
ries. 

7-     The  pulmonary  veins. 

a.  Trace  them  from  the  left  auricle  to  the  lungs. 
Examine  the  left  auricle  carefully  and  find  the 
opening  of  the  common  pulmonary  vein  into  it. 

G.     THE  NERVOUS  SYSTEM  OF  THE  FROG. 

i.  The  method  of  exposing  the  brain  and  spinal  cord. — 
Take  a  frog  which  has  been  a  day  or  two  in  spirit; 
divide  the  skin  along  the  middle  of  the  dorsal  sur- 
face from  the  snout  to  the  anus  and  reflect  it  to 
each  side,  noting  the  small  nerves  running  into  it 
on  each  side  of  the  middle  line ;  remove  the  muscles 
lying  on  the  arches  of  the  vertebra;  open  the  neural 
canal  by  dividing  the  membrane  between  the  atlas 
and  occiput;  then  introduce  one  blade  of  a  small, 
but  strong,  pair  of  scissors  into  the  cranial  cavity, 
and  cut  away  bit  by  bit  the  bones  which  form  the 
roof  of  the  skull,  taking  care  that  the  point  of  the 
scissors  does  not  injure  the  brain.  Next  remove 
the  upper  part  of  the  arches  of  the  vertebrae  in  a 
similar  manner.  A  delicate  pigmented  membrane 
(the  pia-mater)  is  now  laid  bare,  covering  the  brain; 


xiii.]  THE  FROG.  239 

over  the  spinal  cord  it  is  usually  concealed  by  a 
quantity  of  soft  material ;  gently  remove  this  with  a 
pair  of  forceps  or  wash  it  away  with  a  syringe. 

2.     The  brain. 

On  the  dorsal  aspect  of  the  brain,  which  is 'now  ex- 
posed, the  following  parts  will  be  seen ; — 

a.  In  front,  two  elongated  masses  forming  about 
the  anterior  half  of  the  brain:  a  slight  trans- 
verse depression  divides  each  into  an  anterior 
smaller  and  a  posterior  larger  portion.  The 
inner  faces  of  the  anterior  portions  are  closely 
united  together;  those  of  the  posterior  portions 
are  separated  by  a  cleft.  The  posterior  por- 
tions are  the  cerebral  hemispheres  {prosencepha- 
lon};  the  anterior,  the  bases  of  the  olfactory 
lobes  (rhinencephalon). 

a.  The  olfactory  lobes  become  narrowed  into  two 
rounded  trunks  (commonly  termed  the  olfactory 
nerves),   which  leave   the   skull,    and   applying 
themselves  to  the  outer  face  of  the  lining  mem- 
brane of  the  nasal  chamber,  give  off  a  number 
of  branches  which  are  distributed  on  that  mem- 
brane. 

b.  The  thalamencephalon:  lying  between  the  pos- 
terior ends  of  the  cerebral  hemispheres:  on  it 
are  to  be  noticed — 

a.  The  pineal gland ' :  a  very  small  mass  in  front; 
not  composed  of  nervous  tissue. 

(3.  The  thalami  optici:  the  nervous  masses  seen 
below  the  pineal  gland :  between  them  lies  a 
narrow  cavity,  the  third  ventricle. 


2-jo  ELEMENTARY  BIOLOGY.  [CHAP. 

c.  The     optic    lobes    (mesencephalon) :    a    pair    of 
rounded  eminences  lying  behind  the  thalamen- 
cephalon. 

d.  The  cerebellum  (metencephaloji)\  a  narrow  trans- 
verse band  lying  behind  the  optic  lobes. 

e.  The  medtilla  oblongata  (myeloncephalon) :  the  por- 
tion of  the  brain  lying  behind  the  cerebellum. 

a.  Lying  on  the  medulla  oblongata  is  a  trian- 
gular depression  (4th  ventricle}  with  its  apex 
turned  backwards. 

3-     The  spinal  cord. 

a.  Its  form:  wide  in  front,  but  narrowing  rapidly 
about  the  5th  or  6th  vertebra,  and  thence  con- 
tinued  along  the   neural  canal    as   a   slender 
tapering  filament. 

b.  The  groove  (posterior  fissure)  running  along  its 
middle  line. 

c.  The  spinal  nerves  arising  from  it. 
a.      Ten  on  each  side. 

(3.  Each  arising  by  two  roots  (anterior  and  poste- 
rior)-, these  are  most  easily  seen  in  the  7th, 
8th  and  pth  nerves,  where  they  are  much 
longer  than  in  the  others.  Sometimes  the 
anterior  root  is  double. 

y.  The  direction  of  the  roots :  directly  outwards 
in  anterior  nerves;  obliquely  backwards  in 
the  4th,  5th  and  6th;  almost  directly  back- 
wards for  a  considerable  distance  in  the  neu- 
ral canal  in  the  7th,  8th,  Qth  and  loth. 


xni.]  THE  FROG. 


441 


8.  The  point  of  union  of  the  roots  to  form  a 
nerve  trunk,  in  the  intervertebral  foramina. 

Draw  the   exposed  parts  of  the  brain  and  spinal 
cord. 

.  Divide  the  olfactory  lobes,  and  raise  the  front  end 
of  the  brain;  turning  it  back  gradually,  divide  with 
a  sharp  scalpel  any  nerves  that  are  seen  running 
from  it  to  the  cranial  walls:  most  of  the  nerves 
being  small,  they  will  probably  be  torn  across  unob- 
served, but  the  large  optic  nerves  will  at  any  rate  be 
seen:  next  divide  the  nerve-roots  of  the  spinal  cord; 
remove  it  and  the  brain  together  and  place  them 
with  the  ventral  side  upwards. 

a.  On  the  under  surface  (base)  of  the  brain  will  be 
seen — 

a.  The  optic  commissure  or  chiasma  opposite  the 
posterior  end  of  the  cerebral  hemispheres; 
with  the  optic  nerves  diverging  from  its  ante- 
rior end  and  the  optic  tracts  entering  it  poste- 
riorly. 

(3.  Lying  behind  the  optic  commissure,  between 
the  optic  tracts,  is  a  small  eminence — the 
pituitary  body. 

y.  On  each  side  of  the  two  last-mentioned  struc- 
tures and  arched  over  in  front  by  the  optic 
tracts,  are  the  crura  cerebri. 

b.  Divide  the  cerebral  hemispheres  horizontally  with 
a  sharp  scalpel :  in  each  will  be  found  a  cavity — 
the  lateral  ventricle.    Each  lateral  ventricle  com- 
municates with  the  third  ventricle.     The  optic 
lobes,  divided  in  the  same  way,  will  be  seen  to 

M.  l6 


*  ELEMENTARY  BIOLOGY.  [CHAP. 

roof  over  a  cavity  which  communicates  with  the 
third  ventricle  in  front,  and  with  the  fourth 
ventricle  behind. 

c.       The  spinal  cord. 

a.  The  anterior  fissure  running  along  its  ventral 
surface. 

P.  Its  form:  subcylindrical ;  wider  from  side  to 
side  (especially  opposite  the  second  pair  of 
nerves)  than  dorso-ventrally. 

y.  Imbed  it  in  paraffin  and  cut  a  transverse  sec- 
tion :  mount  in  glycerine,  and  examine  with  i 
inch  obj.;  note  its  peripheral  portion  (white 
matter)  different  in  appearance  from  the  cen- 
tral parts  (grey  matter) :  the  canal  (canalis 
centralis)  running  up  its  centre. 

5.  Turn  the  frog  over  en  to  its  back,  lay  open  its  abdo- 
minal cavity  and  remove  all  the  alimentary  canal 
from  the  gullet  to  the  rectum,  along  with  the  liver, 
kidneys  and  generative  organs. 

6.  The  sciatic  plexus. 

a.  This  is  now  seen  as  a  number  of  large  nerve- 
cords  on  each  side  of  the  dorsal  aorta;  note 
the  communications  between  the  different  cords 
of  the  same  side. 

b.  Follow  down  the  plexus  on  one  side :  it  ends 
below  in  a  large  trunk  which  is  continuous  with 
the  sciatic  nerve. 

c.  Trace  the  nerve-trunks  forming  the  plexus  up  to 
the  spinal  column.    They  are  continuous  with 
the  7th,  8th,  and  9th  spinal  nerves. 


xiii.]  THE  FROG.  243 

7.  In  front  of  the  sciatic  plexus — lying  on  the  muscles 
bounding  posteriorly  the  abdominal  cavity — are  three 
nerves  running  obliquely  downwards  and  outwards  on 
each  side:  they  are  continuous  with  the  4th,  5th  and 
6th  spinal  roots. 

8.  Some  nerves  of  the  neck. 

a.  Pass  a  piece  of  tubing  down  the  gullet  so  as  to 
distend  it :  and  then  carefully  remove  the  mylo- 
hyoid  muscle  (B.  6.  a). 

b.  Find  the  posterior  cornu  of  the  hyoid  bone  on 
one  side :  from  it  a  slip  of  muscle  (petrohyoia) 
will  be  seen  passing  up  towards  the  occipital 
region  of  the  skull.     Lying  along  the  posterior 
border  of  this  muscle  is  the  pneumogastric  nerve; 
follow  its  branch  to  the  heart. 

c.  Lying  on  the  petrohyoid  and  in  front  of  the 
pneumogastric,  from  which  it  arises,  is  the  laryn- 
geal  nerve. 

d.  Some  way  in  front  of  the  laryngeal  nerve  is  seen 
the  glossopharyngeal  nerve,  turning  up  towards 
the  front  of  the  jaw. 

e.  Superficial  to  the  glossopharyngeal,  but  with  a 
generally  similar  direction,   is  the  hypoglossal 
ntrve  (B.  6.  a). 

9.  The  brachial  nerve. 

Lay  it  bare  in  the  arm-pit  and  follow  it  back  to  the 
spinal  cord  :  it  is  formed  by  the  union  of  the  2nd  and 
3rd  spinal  nerves. 

10.  The  sympathetic  system. 

a.      Gently  raise  the  aorta:  along  each  side  of  it  will 
be  found  the  main  sympathetic  trunk.    A  slender 

16— 2 


244  ELEMENTARY  BIOLOGY.  [CHAP. 

cord,  with  enlargements  (ganglia)  on  it  at  in- 
tervals. 

b.  Note  the  branches  passing  between  its  ganglia 
and  the  nerves  of  the  sciatic  plexus. 

c.  Carefully  dissect  out  the  gangliated  cord  for  its 
whole  length:  ten  ganglia,  each  provided  with 
communicating  branches  to  other  (spinal)  nerves, 
will  be  found  on  it. 


II.    THE  ORGANS  OF  SPECIAL  SENSE. 

The  complete  examination  of  these,  especially  as  re- 
gards their  histology,  is  difficult,  and  necessitates  the 
employment  of  niceties  in  manipulation  which  it  would 
be  beyond  the  scope  of  this  work  to  describe,  so  that  in 
the  following  account  attention  is  mainly  given  to  those 
points  which  can  be  made  out  without  the  microscope. 
A  brief  account  of  the  microscopic  structure  of  the  re- 
tina will  however  be  found  below  (J.  h). 

a.    The  Eye. 

i.  Take  an  uninjured  frog  and  examine  its  eye.  It  will 
normally  be  found  to  project  considerably  above  the 
top  of  the  head,  but  if  touched  it  is  withdrawn  into 
a  sort  of  socket.  If  the  animal's  mouth  be  opened, 
an  elevation,  caused  by  the  eye-ball,  will  be  seen  on 
its  roof,  and  this  is  more  prominent  when  the  eye-ball 
is  retracted. 

a.  Gently  touch  the  eye  and  observe  how  it  is  closed, 
by  the  pulling  over  it  of  the  lower  transparent 
eye-lid.  The  upper  eye-lid  is  very  small  and 
hardly  moveable.  •:  * . » 


xiii.]  THE  FROG.  245 

I.  When  the  eye  is  open,  observe  the  parts  ex- 
posed. 

a.  The  transparent  cornea  covering  all  its  exposed 
surface. 

(3.  Through  the  cornea  is  seen  the  iris,  a  mem- 
brane coloured  by  brown  and  golden  pigment, 
the  latter  forming  a  very  brilliant  ring  around 
the  inner  margin  of  the  iris.  The  lower  mar- 
gin of  this  ring  is  interrupted  at  one  point, 
the  yellow  pigment  being  there  absent,  and 
from  the  break  a  faint  dark  line  can  be  traced 
downwards  through  the  rest  of  the  lower  part 
of  the  iris. 

y.  The  elliptical  opening  or  pupil  in  the  middle 
of  the  iris  with  its  long  axis  directed  antero- 
posteriorly. 

2.  Kill  the  frog  (by  chloroform  or  by  pithing),  and  care- 
fully dissect  away  the  parts  from  around  the  eye-ball, 
cutting  away,  with  the  rest,  the  part  of  the  upper  jaw- 
bone which  forms  the  lower  boundary  of  the  socket 
of  the  eye-ball,  or  the  orbital  cavity. 

a.  As  the  surrounding  tissues  are  cleared  away 
from  the  eye-ball,  notice  the  small  muscles 
which  are  inserted  into  it. 

J3.  At  the  back  of  the  eye-ball  and  passing  into  it 
will  be  found  the  optic  nerve. 

3.  Divide  the  optic  nerve  and,  having  thus  detached  the 
eye,  pin  it  to  a  piece  of  loaded  cork,  with  the  corneal 
surface  upwards. 

a.  Notice  the  more  opaque  coat  (sclerotic),  with 
which  the  margin  of  the  cornea  is  continuous, 


246  ELEMENTARY  BIOLOGY.  [CHAP. 

and  which  forms  the  outer  envelope  of  the  eye- 
ball on  its  sides  and  back.  In  some  parts  the 
sclerotic  is  semi-transparent  and  allows  the  pig- 
mented  choroid  coat  (3.  g)  to  be  more  or  less 
distinctly  seen  through  it. 

b.  Prick  the  cornea  with  the  point  of  a  sharp  scalpel, 
taking  care  not  to  injure  the  iris ;  note  the  clear 
aqueous  humour  which  spirts  out,  the  cornea  at 
the  same  time  collapsing. 

c.  Seize  the  cut  edge  of  the  cornea  with  a  fine  pair 
of  forceps  and,  with  sharp  scissors,  carefully  cut 
through  it  all  round  at  the  line  of  junction  with 
the  sclerotic.   The  convex  anterior  surface  of  the 
transparent  crystalline  lens  will  now  be  seen  pro- 
jecting through  the  pupil. 

d.  Place  the  cork  in  a  vessel  of  convenient  size 
and  add  enough  water  to  cover  the  eye.     Then, 
with  sharp  scissors,  cut  away  the  iris,  and  so 
expose  all  the  anterior  surface  of   the   lens. 
Passing  the  point  of  a  scalpel  under  one  edge  of 
the  lens,  gently  tilt  it  out  and  examine  it. 

a.  The  crystalline  lens  of  the  frog  is  nearly  sphe- 
rical but  somewhat  thicker  from  side  to  side 
than  antero-posteriorly.  Its  anterior  surface 
(that  which  projects  into  the  pupil)  is  also  less 
convex  than  its  posterior  surface. 

e>  The  cavity  of  the  posterior  chamber  of  the  eye 
is  now  exposed.  It  is  filled  with  a  gelatinous 
transparent  mass,  the  vitreous  humour,  which 
can  be  seen  if  the  water,  in  which  the  eye  is 
being  dissected,  be  poured  away. 


xni.]  THE  FROG.  247 

f.  Lining  the  posterior  chamber  of  the  eye  is  the 
retina,  which,  from  the  action  of  the  water,  will 
probably  now  be  somewhat  cloudy :  in  the  un- 
altered state  it  is  perfectly  transparent,  allow- 
ing the  choroid  (3.  g)  to  be  seen  through  it. 
With  the  point  of  a  microscope  needle  gently 
raise  the  retina  from  the  black  membrane  (cho- 
roid) beneath  it.     It  will  be  found  that  this  can 
be  readily  done  except  at  one  point  (answering  to 
the  blind  spot  of  our  own  eyes),  which,  by  turning 
the  eye-ball  over  will  be  seen  to  be  opposite  the 
point  of  entrance  of  the  optic  nerve  (2.  /?). 

g.  The  choroid  coat  of  the  eye-ball  is  now  exposed. 
It  is  a  dark  pigmented  membrane,  of  loose  floccu- 
lent  texture,  which  can  be  readily  detached,  by 
needles,  from  the  sclerotic  which  lies  outside  it. 

b.    The  Ear. 

i.  The  frog  has  no  external  ear,  its  tympanic  membrane, 
as  already  mentioned  (A,  2.  a),  being  exposed  on  each 
side  of  the  head. 

a.  Note  the  arrangement  of  the  tympanic  mem- 
brane :  it  is  smoothly  stretched  over  a  hard  ring. 

Dissect  away  the  outer  or  integumentary  layer 
of  the  tympanic  membrane.  Beneath  it  will  be 
found  a  transparent  membrane,  formed  by  the 
fibrous  and  mucous  layers,  with  an  opaque  white 
patch  about  its  middle. 

c.  Cut  through  these  layers  of  the  tympanic  mem- 
brane along  their  margins  :  the  tympanic  cavity 
will  then  be  laid  open. 


b. 


ELEMENTARY  BIOLOGY.  [CHAP. 

a.  The  tympanum  of  the  frog  is  a  funnel-shaped 
cavity  with  its  wider  end  turned  outwards. 
Its  sides  are  bounded  by  a  smooth  slightly  pig- 
mented  mucous  membrane,  continuous  with 
that  of  the  mouth  through  the  Eustachian 
recess. 

/?.  In  its  roof  lies  a  rod,  ossified  in  the  middle, 
cartilaginous  at  each  end,  which  is  the  columetta 
auris.  The  columella  is  attached,  by  its  inner 
end,  to  the  upper  and  anterior  part  of  the 
inner  wall  of  the  tympanum  and,  by  its  outer 
end,  to  the  middle  layer  of  the  tympanic 
membrane,  in  the  region  of  the  opaque  patch 
mentioned  above  (i.  b). 

y.  Close  to  the  inner  attachment  of  the  columella 
there  is  a  comparatively  large  oval  opening  in 
the  wall  of  the  tympanic  cavity ;  this  is  the 
outer  end  of  the  Eustachian  recess,  the  inner 
end  of  which  has  been  already  (B.  n.  a)  seen 
on  the  posterior  part  of  the  roof  of  the  mouth. 
Pass  a  probe  through  the  opening  now  ex- 
posed, and  open  the  frog's  mouth  to  see  its 
passage  into  that  cavity. 

2.      The  internal  ear. 

a.  Carefully  dissect  away  the  columella  auris  from 
its  inner  attachment.    An  aperture  into  which  it 
was  inserted  will  thus  be  exposed :  this  is  the 
fenestra  ovalis. 

b.  Take  a  pair  of  scissors  and  cut  through  the 
bones  of  the  side  of  the  skull  in  a  line  joining 
the  fenestra  ovalis  and  the  "  guard  "  of  the  para- 


xiir.]  THE  FROG.  24Q 

sphenoid  bone  (D.  c.  3.0);  the  chamber  in  the 
pro-otic  bone  (D.  c.i.d)  which  is  thus  exposed 
contains  part  of  the  internal  ear. 

c.  The  dissection  of  the  internal  ear  of  the  frog 
is  difficult,  on  account  of  its  minuteness.  But 
by  carefully  removing  the  bony  and  cartilagi- 
nous walls  of  the  periotic  capsule,  piecemeal, 
the  semicircular  canals  will  be  exposed  and  the 
whole  membranous  labyrinth  may  be  extracted. 
It  should  be  placed  in  a  watch-glass  containing 
salt  solution  or  spirit,  and  its  form  studied  under 
the  simple  microscope. 

c.      The  olfactory  organs. 

i.  These  consist  of  two  chambers  which  open  externally, 
near  the  end  of  the  snout,  by  the  anterior  nares,  and 
posteriorly  into  the  mouth,  just  behind  the  vomerine 
teeth  by  the  posterior  nares.  Make  out  these  open- 
ings. 

a.  Take  a  frog  which  has  been  preserved  in  spirit 
and  pass  the  point  of  a  small  pair  of  scissors  into 
the  external  nostril  of  one  side  and  cut  away  the 
roof  of  the  nasal  cavity.     A  chamber  is  thus  ex- 
posed which  has  a  somewhat  triangular  form,  the 

'  •  apex  of  the  triangle  being  at  the  external  nostril 

and  the  posterior  nostril  being  at  another  angle 
and  farther  from  the  middle  line. 

b.  The  walls  of  the  cavity  are  slightly  folded,  and 
there  is  a  well-marked  hemispherical  eminence 
on  its  floor. 

c.  Open  the  other  nasal  cavity  in  a  similar  way: 
notice  the  boundary  wall  (septum  narium)  which 


250  ELEMENTARY  BIOLOGY.  [CHAP. 

lies  between  the  two  and  completely  separates 
them. 

d.  Open  the  nasal  cavity  of  a  frog  which  has  been  pre- 
served in  Muller's  fluid  ;  gently  scrape  away  a  little 
of  the  epithelium  lining  the  chamber,  mount  in 
water :  examine  with  your  highest  power. 

a.  Among  numerous  mutilated  cells,  a  certain  num- 
ber of  more  or  less  perfect  ones  will  be  found  : 
these  are  of  two  kinds,  viz.  large  columnar  epi- 
thelial cells  (J.  i.  £),  each  with  an  oval  nucleus, 
an  unbranched  peripheral  process  and  a  branched 
deeper  one  ;  and  smaller  cells,  with  less  proto- 
plasm around  the  nucleus  and  finer  peripheral 
and  central  processes. 

d.    The  gustatory  organ. 

i.      The  shape  and  arrangement  of  the  frog's  tongue  have 
already  been  described  (B.  11.0). 

a.  Snip  off  a  bit  of  mucous  membrane  from  the 
upper  surface  of  the  tongue  of  a  recently  killed 
frog,  mount  in  normal  saline  solution  and  cover 
in  plenty  of  the  fluid  with  a  large  coverslip  :  ex- 
amine with  one  inch  obj. 

a.  On  the  surface  of  the  fragment  and  especially 
around  its  edges  numerous  minute  elevations 
of  the  surface  will  be  seen  :  these  are  the/#- 
pilfa:  some  (filiform  papillcz)  are  pointed  at 
the  free  end  and  others  (fungiform  papilla) 
flattened.  Note  the  loops  which  the  blood 
capillaries  make  in  some  of  the  papillae. 

p.  Examine  one  of  the  thinner  bits  of  the  speci- 
men with  a  higher  power  :  the  papillae  will  be 
seen  to  be  covered  by  epithelium,  which  is  for 


xiil.]  THE  FROG.  251 

the  most  part  ciliated  (J.  i.  c) ;  some  of  the 
papillae  however  will  be  seen  to  have  no  cilia 
except  a  narrow  belt  around  the  somewhat 
truncated  apex ;  it  is  on  these  latter  papillae 
that  the  gustatory  discs  are  placed,  and  in 
fortunate  specimens  nerve-fibres  can  be  seen 
entering  them. 

J.      SOME  OF  THE  MORE   IMPORTANT  POINTS    IN  THE  HISTO- 
LOGY OF  THE  FROG. 

a.    Epithelium.  , 

i.  This  consists  of  cells  which  line  free  surfaces  within 
the  body :  the  epidermis  covering  the  skin  is  a  simi- 
lar structure,  and  is  continuous  with  epithelium  at 
the  apertures  of  the  body.  There  are  several  main 
types  of  epithelium,  viz. — • 

a.  Scaly  epithelium.  Open  the  abdomen  of  a  re- 
cently killed  frog,  carefully  remove  the  viscera 
and  lay  bare  the  lymph  sinus  at  the  back  of  the 
body-cavity.  Cut  away  its  thin  wall  as  care- 
fully as  possible,  taking  great  care  not  to  drag  or 
pull  it.  Place  the  fragment  in  0-5^  solution  of 
silver  nitrate  for  about  three  minutes :  then 
remove,  wash  well  in  distilled  water,  and  finally 
leave  the  specimen  in  distilled  water  and  ex- 
posed to  the  sunlight.  So  soon  as  the  bit  of 
pleuroperitoneum  has  become  of  a  well-marked 
brown  colour,  mount  it  in  glycerine  and  exa- 
mine with  a  high  power. 

a.  It  will  be  seen  to  be  covered  on  both  sides 
with  flat  closely  fitting  cells,  the  boundary 
lines  of  which  are  stained  black  by  the  sil- 


25*  ELEMENTARY  BIOLOGY.  [CHAP. 

ver;  according  to  the  amount  of  staining  a 
nucleus  may  or  may  not  be  rendered  conspi- 
cuous in  each  cell. 

Here  and  there  in  good  specimens,  rings 
of  smaller  and  more  deeply  stained  cells  will 
be  seen  surrounding  minute  apertures  (sto- 
mata). 

I.  Columnar  epithelium.  Scrape  gently  the  inner 
surface  of  the  mucous  membrane  of  the  intes- 
tine of  a  frog  which  has  been  preserved  in 
Miiller's  fluid;  mount  the  detached  fragments 
in  water  and  examine  with  a  high  power. 

a.  Numerous  elongated  cells,  flat  at  one  end 
and  somewhat  pointed  at  the  other,  will  be 
seen.  Each  has  a  well-marked  oval  nucleus. 

J3.  These  cells  may  be  seen  in  situ  if  a  thin  sec- 
tion of  the  hardened  mucous  membrane  of 
the  intestine  or  stomach  be  examined.  They 
are  closely  applied  and  arranged  in  a  single 
layer. 

c.  Ciliated  epithelium.  Snip  off  a  bit  of  the  mucous 
membrane  from  the  tongue  of  a  recently  killed 
frog  with  a  sharp  pair  of  scissors :  mount  the 
bit  in  07 5^-  sol.  of  sodic  chloride,  avoiding 
pressure,  and  examine  with  a  high  microscopic 
power. 

a.  Note  the  shimmering  appearance  along  its 
free  edge,  produced  by  the  rapidly  moving 
cilia;  as  the  cilia  begin  to  die  and  their 
movement  slackens,  individual  ones  can  be 
seen. 


xiii.]  THE  FROG.  253 

^.  Scrape  gently,  with  a  scalpel,  one  of  the  pro- 
minences in  the  roof  of  the  frog's  mouth  be- 
neath the  eye-balls:  mount  the  scrapings  in 
075  salt  solution  and  examine  with  -J  objec- 
tive for  individual  ciliated  cells ;  note  their 
roundish  form,  granular  protoplasm  and  nu- 
cleus, and  the  group  of  cilia  borne  on  one 
end ;  stain  with  iodine. 

b.  Cartilage. 

i.      Dissect  out  carefully  the  omosternal  or  xiphisternal 
cartilage  of  a  recently  killed  frog;  mount  in  075 J 
sodic  chloride  solution  and  examine  with  ^  or  |  obj. 
a.      Large    roundish    granular    cartilage-cells  will 
be  seen  imbedded  in  a  structureless  or  very 
finely  granular  matrix,  which  is  more  refrac- 
tive next  the  cells  than  elsewhere,  and  causes 
the  appearance  of  a  sort  of  halo  round  each. 

(3.  In  each  cell  lies  a  distinct  granular  round 
nucleus  or  sometimes  two  nuclei,  containing 
large  highly  refractive  molecules. 

y.  If  the  preparation  be  carefully  made,  each 
cell  will  at  first  completely  fill  the  cavity  of 
the  matrix  in  which  it  lies,  but  if  it  be  kept 
some  time  or  be  treated  with  distilled  water 
the  cells  contract  and  so  leave  a  transparent 
ring  between  their  surface  and  the  inside  of 
the  cavity  in  which  each  lies. 

c.  Bone. 

a.  Examine  a  prepared  transverse  section  of  hard 
bone  (say  a  bit  of  the  shaft  of  the  humerus  or 
femur)  with  i  inch  obj.  A  bit  of  mammalian 


254  ELEMENTARY  BIOLOGY.  [CHAP. 

bone  is  the  best  for  seeing  the  essential  struc- 
ture. 

a.  The  Haver sian  canals:  round  or  oval  spaces, 
usually  rilled  with  dirt  in  grinding  down  the 
bone,  and  therefore  black  and  opaque,  but 
sometimes  clear  and  empty. 

ft.  The  lamella:  a  series  of  concentric  layers 
round  each  Haversian  canal. 

y.  The  lacuna:  oval  black  spots  between  the 
lamellae. 

8.  The  canaliciili :  minute  black  lines  seen  radi- 
ating from  the  lacunae. 

€.  Besides  the  lamellae  above  mentioned  others 
will  be  seen  which  belong  to  no  Haversian 
system,  but  either  fit  in  the  angles  between 
the  systems,  or  run  around  the  outer  surface 
of  the  bone. 

b.  Examine  with  \  obj.     Observe  the  lacunae  and 
canaliculi  more  accurately. 

c.  Examine  in  water  or  glycerine  a  thin  transverse 
section  of  a  long  bone  which  has  been  softened 
by  dilute  acid. 

a.  The  Haversian  canals  empty  or  containing  a 
granular  mass. 

ft.      The  lamella:  very  indistinct. 

y.      The  lacuna  seen  as  transparent  oval  spaces. 

8.      The  canaliculi  transparent  and  almost  invisible. 

d.  Examine  sections  of  softened  bone  which  have 
been  stained  with  carmine :  in  each  lacuna  will 
be  found  a  stained  mass  of  protoplasm. 


xiii.]  THE  FROG.  255 

c.  Examine  longitudinal  sections  of  the  femur  or 
humerus :  the  Haversian  canals  are  seen  to  be 
channels  running  for  the  most  part  in  the  long 
axis  of  the  bone,  but  communicating  with  one 
another  frequently  by  cross  branches.  The 
lacuna,  &c.  appear  much  as  in  the  transverse 
section. 

d.    Connective  tissue. 
i.     Of  this  there  are  two  main  varieties,  viz. — 

a.  White  fibrous  tissue.      This  occurs  nearly  pure  in 
tendons,   but  is  widely  distributed  throughout 
the  body,  mixed  with  other  tissues.     Tease  out 
a  bit  of  fresh  tendon  in  water:   examine  with  a 
high  power. 

a.  It  is  chiefly  made  up  of  very  fine  wavy  fibres 
which  run  in  bundles  parallel  to  one  another; 
they  have  an  ill-defined  outline  and  do  not 
branch. 

/5.  Treat  with  dilute  acetic  acid.  Most  of  the 
fibres  disappear,  but  a  few  well-defined  curled 
fibres  (yellow  elastic  fibres,  see  b)  remain.  Be- 
sides these  some  elongated  granular  proto- 
plasmic masses  are  brought  into  view  (con- 
nective-tissue corpuscles]. 

b.  Yellow  elastic  tissue.   This  does  not  occur  in  large 
collections,  in  the  pure  form,  in  the  frog;  although 
mixed  with  white  fibrous  and  other  tissues,  it  is 
very  widely  distributed. 

a.  Tease  out  in  acetic  acid  some  of  the  bands  of 
tissue  beneath  the  frog's  skin;  examine  with 
a  high  power.  Numerous  fine  well-defined 


2  5 6  ELEMENTAR  Y  BIOL  OGY.  [c HAP. 

branched  fibres,  running  in  bold  curves,  will  be 
seen:  these  are  yellow  elastic  fibres,  as  the 
acetic  acid  (a.  /?)  destroys  the  white  fibrous 
tissue. 

e.    Striped  muscle. 

a.  Tease  out  gently  a  bit  of  muscle  which  has  been 
kept  in  alcohol,  and  examine  with  i  inch  obj. 

a.  Composed  of  elongated  fibres,  which  exhibit 
a  tendency  to  split  up  into  finer  filaments 
(fibrilfo). 

b.  Examine  with  high  power. 

a.  The  alternate  lighter  and  darker  bands  placed 
transversely  to  the  long  axis  of  the  fibre 
(transverse  striatiori). 

/3.  The  fine  structureless  membrane  (sarcolemma) 
enveloping  the  fibre :  seen  here  and  there  as 
a  delicate  film  where  the  fibre  is  twisted  or 
bruised. 

y.      The  tendency  to  split  up  into  fibrillae. 

c.  Tease  out  a  bit  of  fresh  muscle  in  075 -J  so  die 
chloride  solution. 

a.  The  transverse  striation  of  the  fibres:  less 
distinct  than  in  the  muscle  from  alcohol. 

/?.  The  absence  of  a  tendency  to  split  up  into 
nbrilte. 

y.  The  sarcolemma,  which  may  be  seen  at 
points  where  the  continuity  of  its  contents 
has  been  interrupted  by  pressure,  twisting, 
&c. 


xiii.]  THE  FROG.  257 

8.  Treat  with  acetic  acid :  the  striation  rendered 
very  indistinct;  oval  nuclei  made  apparent 
here  and  there  in  the  fibre. 

f.    Nerve-fibres. 

i.  Tease  out  a  bit  of  fresh  nerve  in  07 5 §-  sodic  chlo- 
ride. Examine  with  a  high  power. 

a.  Composed   of  well-defined   fibres  (white  nerve 
fibres]  mixed  with  white  fibrous  tissue  (d.  i.  a). 

b.  The  appearance  of  the  nerve-fibres:    each  has 
a  double  contour,   marked  out   by  a  curdled- 
looking  highly  refractive  border  on  each  side. 

c.  The  structure  of  the  nerve-fibres. 

a.  The  delicate  structureless '  investing  mem- 
brane (primitive  sheath]',  look  for  it  on 
bruised  nerve-fibres  or  at  the  ends  of  torn 
fibres. 

/?.  The  highly  refractive  border  (medullary 
sheatK]  within  the  primitive  sheath. 

y.  The  central  homogeneous  axis  (axis,  cylinder); 
look  for  it  projecting  beyond  the  medullary 
sheath  of  torn  fibres. 

d.  Treat  a  fresh  bit  of  teased-out  nerve  with  chlo- 
roform: the  medullary  sheath  will  be  dissolved 
out,  and  the  axis  cylinder  plainly  seen. 

£.    Nerve-cells. 

i.  Take  a.  sympathetic  ganglion  from  a  recently  killed 
frog:  dissect  out  in  normal  saline  solution  and  ex- 
amine with  ~  obj. 

a.  Among  the  pigment-cells,  which  are  clustered 
around  the  ganglion,  will  be  seen  numerous 

M.  I? 


258  ELEMENTARY  BIOLOGY.  [CHAP. 

large  pale  granular  cells,  each  possessing  a 
conspicuous  clear  round  nucleus  with  a  dis- 
tinct nucleolus. 

/?.  Tease  out  in  glycerine  a  Gasserian  ganglion 
from  a  frog's  head  which  has  been  preserved 
in  Miiller's  fluid  or  chromic  acid.  Cells  like 
those  described  above  will  be  found. 

y.  Examine  sections  of  spinal  cord  which  have 
been  stained  with  carmine  or  hsematoxylin, 
and  note  the  large  branched  nucleated  cells 
in  the  grey  matter  especially  towards  the  ven- 
tral side  of  the  cord. 

h.    The  retina. 

j.  Sufficiently  satisfactory  specimens  of  this  organ  can 
be  obtained  as  follows.  Take  perfectly  fresh  eyes 
from  a  frog,  prick  the  corneas  in  two  or  three  places, 
and  lay  the  eyes  aside  for  three  or  four  days  in  o'25§ 
chromic  .acid  solution:  then  transfer  them  to  alcohol 
and  keep  them  in  it  until  wanted. 

a.  Carefully  cut  open  an  eye  preserved  in  the 
above  method  and  expose  the  retina:  transfer 
the  latter  to  a  glass  slide,  and  with  a  razor  chop 
down  on  it  so  as  to  cut  off  a  number  of  slices : 
add  glycerine,  put  on  a  cover,  and  examine 
with  a  low  power.  Some  of  the  bits  will  be 
found  thin  enough  for  further  examination. 

I.  With  the  low  power  little  can  be  seen  but  that 
the  retina  is  composed  of  a  number  of  different 
layers,  some  of  which  appear  less  opaque  than 
the  others. 


XIIL]  THE  FROG.  759 

c.      Put  on  a  high  power  and  examine,  make  out 

the  following  points — 

a.  The  internal  limiting  membrane,  a  thin  struc- 
tureless layer. 

ft.      The  nerve-fibre  layer:  thin  and  granular. 

[Both  o  and  0  are  often  difficult  to  make  out  in 
retinas  prepared  as  above.] 

y.  The  nerve-cell  layer:  composed  mainly  of  cells 
like  those  described  above  (g.  i.  a),  but  rather 
smaller  than  those  from  the  sympathetic 
ganglia.  From  some,  branches  can  be  traced 
into  the  next  layer. 

S.  The  molecular  layer:  this  is  thicker  than  any 
of  the  preceding,  and  has  a  finely  punctated 
appearance :  running  through  it  the  fibres  of 
Miiller  (h.  i.  i)  are  very  plainly  seen. 

e.  The  inner  granular  layer:  this  is  the  layer 
which  usually  looks  clearest  in  sections,  its 
elements  being  less  closely  packed  than  those 
of  the  other  layers.  It  is  made  up  of  a  num- 
ber of  nuclei  (which  in  chromic-acid  speci- 
mens look  granular),  around  which  is  col- 
lected a  very  small  amount  of  protoplasm, 
and  of  fine  fibres,  some  of  which  can  be 
traced  joining  the  nuclei  or  granules. 

£.  The  inter-granular  (fenestrated}  layer.  A  nar- 
row cloudy  layer  in  which  no  definite  struc- 
tural elements  are  visible. 

77.  The  outer  granular  layer.  Much  thinner  than 
the  inner  granular  layer  and  more  closely 
packed.  It  is  composed  of  distinct  fibres 

17—2 


160  ELEMENTARY  BIOLOGY.  [CHAP. 

(rod-  and  cone-fibres),  each  of  which  swells  out 
and  has  a  nucleus  (the  granule)  developed  in 
the  enlargement. 

0.  The  external  limiting  membrane.  A  thin 
homogeneous  layer  like  a. 

t.  The  fibres  of  Mutter.  These  are  highly  re- 
fracting fibres  which  can  be  traced  with  ease 
from  the  internal  limiting  membrane  to  the 
fenestrated  layer.  They  probably  run  beyond 
the  latter  and  end  on  the  external  limiting 
membrane,  but  are  difficult  to  trace  through 
the  outer  granular  layer. 

K.  The  rod-  and  cone-layer.  The  main  thing 
which  will  be  noted  here  is  the  huge  rods  for 
the  most  part  distorted  by  the  treatment 
to  which  the  retina  has  been  exposed.  In 
favourable  bits  it  can  be  seen  that  each  rod 
is  divided  transversely  into  an  inner  and  an 
outer  segment.  The  cones  are  few  and  small, 
and  generally  completely  concealed  by  the 
rods. 

d.  Take  a  fresh  .frog's  eye:  prick  its  cornea  and 
collect  the  aqueous  humour  on  a  slide.  Then 
open  the  eye,  remove  a  bit  of  the  retina  and 
tease  it  out  in  the  aqueous  humour,  mount  and 
examine  with  a  high  power. 

a.  Numerous  rods  will  be  seen  floating  about, 
many  broken  but  some  intact  and  shewing  the 
boundary  line  between  their  two  segments  very 
plainly.  At  first  both  segments  are  homoge- 
neous, but  very  soon  they  begin  to  alter ;  the 


xni.]  THE  FROG.  261 

outer  layer  frequently  then  getting  a  trans- 
versely striated  appearance  and  shewing  a 
tendency  to  split  up  into  corresponding  pieces  : 
gradually  these  rods  entirely  disintegrate,  first 
curling  up,  swelling  out,  &c. 

i.    The  skin. 

1.  Cut  out  a  piece  of  skin  from  the  back  of  the  thigh  of 
a  recently  killed  frog :  spread  it  out  in  water,  cover, 
and  examine  with  a  low  power  :  note — 

a.  The  pigment  -  cells ;    seen   as   black   irregularly 
shaped  patches;  some  compact,  others  more  or 
less  branched. 

b.  The  months  of  the  cutaneous  glands ;   seen  as 
clear  round  spots,  although  their  openings  are 
really  triradiate  :  their  number. 

2.  Take  a  piece  of  skin  that  has  lain  for  a  day  or  two  in 
solution  of  ammonia  bichromate  and  then  in  alcohol : 
imbed  it,  and  cut  sections  perpendicular  to  its  sur- 
faces :   mount   in   glycerine.     Examine   with  a  low 
power;  note — 

a.  The  two  layers  of  the  skin,  dermis  and  epidermis, 
the  former  being  much  the  thicker  :  note  in  the 
dermis  its  deeper  connective-tissue  layer,  and 
its  more  superficial  granular  layer  immediately 
beneath  the  epidermis. 

b.  Examine  with  a  higher  power. 

u.  The  epidermis  is  seen  to  be  made  up  of  nume- 
rous closely  packed  cells,  arranged  in  several 
layers. 

fi.     The  deepest  epidermic  cells  are  granular,  nu- 


262  ELEMENTARY  BIOLOGY.  [CHAP. 

cleated,  and  somewhat  oval,  with  their  long 
axes  at  right  angles  to  the  surface. 

y.  Then  come  several  rows  of  cells,  also  granular 
and  nucleated,  but  becoming  smaller  and 
rounder  as  they  become  more  superficial. 

8.  The  most  superficial  three  or  four  layers  of 
cells  are  flattened  parallel  to  the  surface, 
are  not  granular,  and  possess  no  apparent 
nucleus. 

«.  Here  and  there  a  pigment-cell  is  seen  .among 
the  epidermic  cells,  and  some  of  the  latter 
contain  a  few  pigment-granules. 

£.  The  dermis,  consisting  fundamentally  of  white 
fibrous  and  elastic  tissues :  its  glandular  and 
non-glandular  layers. 

-rj.  Immediately  beneath  the  epidermis  is  a  thin 
stratum  of  connective  tissue  in  which  lie 
many  large  pigment-cells,  sometimes  forming 
an  almost  continuous  layer. 

0.  Then  come  a  large  number  of  round  cavities, 
the   cutaneous  glands,   lined  by  large,   pale, 
slightly  granular,  nucleated  cells,  which  are 
columnar  when  seen  sidewise,  but  polygonal 
when  seen  from  the  base  or  apex.     Some- 
times the  duct  of  the  gland  can  be  traced 
running  from  it  through  the  epidermis.    Sepa- 
rating  the  glands   and    supporting  the  epi- 
thelium are  bundles   of   connective    tissue, 
consisting  mainly  of  fibres  running  perpen- 
dicularly to  the  surface. 

1.  The  deepest  layer  of  the  dermis  is,  made  up 


xiii.]  THE  FROG.  263 

of  connective-tissue  bundles,  running  for  the 
most  part  parallel  to  the  surface. 

j.    The  kidney. 

i.  Take  a  frog's  kidney  which  has  been  for  a  week 
in  solution  of  bichromate  of  potash,  and  then  for  a 
day  or  two  in  spirit.  Imbed  it,  cut  sections  parallel 
to  its  flatter  surfaces,  and  mount  in  glycerine. 

a.  Examine  with  a  low  power. 

a.  Note  the  numerous  tubules  of  which  the  organ 
is  mainly  composed  and  which  twist  about  in 
all  directions,  and  are  consequently  cut,  some 
transversely,  some  obliquely,  and  others  more 
or  less  longitudinally.  The  absence  of  any 
marked  division  into  cortex  and  medulla. 

/?.  The  clear  round  holes,  scattered  about;  these 
are  sections  of  glomeruli  from  which  the  con- 
tained vessels  have  fallen  out.  Some  may  be 
seen  in  which  a  granular  mass  still  lies. 

b.  Examine  with  a  higher  power — 

a.  The  epithelium  lining  the  tubules,  composed 
in  some  of  granular  and  ill-defined  cells,  in 
other  (usually  larger)  tubules  of  clearer  and 
better-defined  cells;  both  varieties  are  nu- 
cleated. 

c.  Examine  specimens  of  injected  kidney  with  a 
low  power.     Note  the  vascular  tufts  of  the  glo- 
merulL 

k.    The  testis. 

i.      Imbed  a  testis  which  has  been  hardened  in  alcohol : 
cut  sections  and  mount  in  glycerine. 


ELEMENTARY  BIOLOGY.  [CHAP. 

a.  Examine,  with  a  low  power. 

a.  The  organ  is  chiefly  made  up  of  tortuous 
tubules,  which  are  seen  cut  in  various  direc- 
tions. 

b.  Examine  with  a  high  power. 

a.  Note  the  epithelium  lining  the  tubules :  it 
varies  with  the  season  of  the  year  (whether 
before  or  after  the  breeding-time),  and  is  usu- 
ally extremely  granular  and  ill-defined.  The 
cells  are  arranged  in  two  or  three  rows,  and 
at  the  time  of  breeding  the  most  superficial, 
layer  of  cells  is  transformed  into  spermatozoa, 
each  cell  giving  rise  to  several.  These  lie 
side  by  side  at  right  angles  to  the  lumen  of 
the  tubule,  which  accordingly  appears  to  be 
lined  by  them. 

c.  The  spermatozoa  (B.  10.  a.  y). 

The  ovary. 

The  structure  of  this  organ  is  easiest  made  out 
shortly  after  the  breeding-time.  Remove  one  of  the 
ovaries,  place  it  in  water,  and  make  an  incision  into 
it :  it  will  be  seen  to  contain  a  cavity,  and  projecting 
upon  the  walls  of  this  cavity  and  also  upon  the  outer 
surface  of  the  ovary  are  numerous  round  eminences 
of  various  sizes :  these  are  ova  in  different  stages  of 
development,  and  the  large  ones  will  be  seen  to  have 
become  more  or  less  pigmented. 

Tease  out  a  bit  of  ovary  in  normal  saline  solution  : 
rover,  and  examine  with  a  low  power. 

a.      Note  the  ova,  many  much  smaller  than  those 
which  were  seen  (i)  with  the  naked  eye  :  they 


xin.]  THE  FROG.  265 

appear  as  granular  spherical  masses  with  a  clearer 
central  patch. 

I.  Examine  with  a  high  power  a  portion  of  your 
specimen  containing  some  of  the  younger  and 
more  transparent  ova.  Note — 

a.  The  thin  structureless  membrane,  vitdline 
membrane,  enveloping  each. 

/?.  The  granular  matter  (yelk,  vitellus)  forming 
most  of  the  ovum.  It  sometimes  appears  to 
be  composed  of  an  outer  granular  and  an 
inner  clearer  layer. 

y.  The  clearer  central  mass  (germinal  vesicle)  im- 
bedded in  the  vitellus.  The  large  number  of 
highly  refracting  masses  (germinal  spots)  within 
the  germinal  vesicle. 

K.    THE  PHYSIOLOGICAL  PROPERTIES  OF  MUSCLE  AND  NERVE. 

Place  a  frog  under  a  beaker,  with  a  drop  or  two 
of  chloroform :  take  it  out  immediately  it  becomes 
unconscious,  which  will  probably  be  in  a  few  se- 
conds. Now  feel  with  a  finger-nail  for  the  depression 
beneath  the  skin  at  the  back  of  the  animal's  head, 
which  indicates  the  point  of  articulation  of  skull  and 
spinal  column  :  it  lies  in  a  line  joining  the  posterior 
borders  of  the  two  tympanic  membranes.  Divide 
the  skin  and  muscles  at  this  point  until  the  neural 
canal  is  laid  open,  and  then  pass  a  stout  wire  into 
the  cranium  and  down  the  neural  canal  of  the  ver- 
tebral column.  By  this  process  (known  as  pithing} 
the  frog  is  rendered  totally  incapable  of  further  con- 
sciousness, though  most  of  its  tissues  will  retain  their 
vitality  for  some  time. 


6  ELEMENTARY  BIOLOGY.  [CHAP. 

a.  Remove  the  skin  from  one  leg,  so  as  to  lay  bare 
the  muscles :  send  an  interrupted  electric  cur- 
rent through  any  one  of  them  (or  tap  the  muscle 
sharply  with  the  back  of  a  scalpel) :  it  will  im- 
mediately contract,  or  alter  its  form  in  a  definite 
way;  it  becomes  shorter  and  thicker,  and  in  so 
doing  moves  the  bones  to  which  it  is  attached. 

b.  Very  carefully  lay  bare  the  sciatic  nerve,  taking 
care  not  to  crush  or  drag  it :  divide  it  as  high 
up  as  possible  and,  seizing  it  with  a  pair  of  for- 
ceps close  to  its  cut  end,  lay  it  over  the  elec- 
trodes of  an  induction-coil.    Probably  when  the 
nerve  is  cut  the  muscles  of  the  limb  will  con- 
tract :  whether  or  not,  however,  they  will  con- 
tract violently  while  the  interrupted  current  is 
going  through  the  nerve. 

[If  an  induction-coil  is  not  at  hand  a  bit  of 
clean  copper  wire  twisted  round  a  strip  of  zinc, 
with  the  points  of  contact  moistened  with  dilute 
acetic  acid,  may  be  used  to  stimulate  the  nerve; 
smart  tapping  or  pinching  with  a  pair  of  forceps 
will  also  excite  it,  but  by  such  means  the  nerve  is 
soon  killed.] 

The  above  experiments  shew: — 

c.  That  the  muscle   is    irritable  and  contractile: 
certain  external  agencies  (stimuli]  excite  some 
change  in  it,  the  result  of  which  is  a  muscular 
contraction. 

d.  The  nerve  is  irritable:  certain  external  agencies 
excite  some  change  in  it,   which  in  this  par- 
ticular case  manifests  itself  by  a  contraction  of 
the  muscles  connected  with  the  nerve. 


xiii.]  THE  FROG.  267 

e.  The  nerve  possesses  conductivity :  although  it  is 
stimulated  at  some  distance  from  the  muscles, 
yet  the  change  excited  by  the  stimulus  travels 
along  it  to  them. 


APPENDIX. 


The  various  re-agents,  mentioned  in  the  "  Laboratory  work" 
in  the  preceding  pages,  are  prepared  as  follows  : 

1.  Acetic  acid,  Dilute. 

Mix  i  cub.  centimetre  of  glacial  acetic  acid  with  99  cub. 
cent,  of  distilled  water. 

2.  Ammonic  bichromate,  Solution  of. 

Dissolve  10  grammes  of  crystallized  ammonic  bichro- 
mate in  a  litre  of  distilled  water. 

3.  Carmine,  Solution  of. 

Carmine 2  grammes. 

Strong  solution  of  ammonia  4  cub.  cent. 

Distilled  water  48  cub.  cent. 

Dissolve  the  carmine  in  the  ammonia  and  water;  leave 
in  an  unstoppered  bottle  until  nearly  all  smell  of  ammo- 
nia has  gone.  Afterwards  keep  in  a  well-closed  bottle. 
Dilute  a  small  quantity  with  fifteen  or  twenty  times  its 
bulk  of  water,  when  required  for  use. 

4.  Chromic  acid,  Solution  of. 

Dissolve  10  grammes  of  crystals  of  chromic  acid  in  one 
litre  of  water.  This  gives  a  i  per  cent,  solution,  from 
which  weaker  ones  can  readily  be  prepared  when  re- 
quired. 


APPENDIX.  rfy 

5.  Hsematoxylin,  Solution  of. 

a.  Prepare  a  saturated  solution  of  crystallized  calcic 
chloride  in  70  per  cent,  alcohol ;  then  add  alum  to 
saturation. 

b.  Prepare  a  saturated  solution  of  alum  in  70  per  cent, 
alcohol.    Add  I  volume  of  a  to  8  of  b. 

c.  To  the  mixture  of  a  and  b  add  a  few  drops  of  a 
saturated  solution  of  pure  hsematoxylin  in  absolute 
alcohol.     Filter. 

6.  Iodine,  Solution  of. 

Prepare  a  saturated  solution  of  potassic  iodide  in  dis- 
tilled water;  saturate  this  solution  with  iodine.  Filter. 
Dilute  to  a  brown  sherry  colour. 

7.  Magenta,  Solution  of. 

Dissolve  I  decigr.  of  crystallized  magenta  (roseine)  in 
160  cubic  centimetres  of  distilled  water:  add  I  cub.  cent, 
of  absolute  alcohol.  Keep  in  a  well-closed  bottle. 

8.  Mayer's  Solution. 
See  note  p.  8. 

9.  Mullens  Solution. 

Bichromate  of  potash 25  grammes. 

Sodic  sulphate 10  grammes. 

Distilled  water I  litre. 

10.  Osmic  Acid,  Solution  of. 

Best  bought  ready  made  in  the  form  of  I  per  cent,  solu- 
tion. 

11.  Paraffin. 

Melt  together  one  part  of  solid  paraffin  (paraffin  candles 
will  do),  one  part  of  paraffin  oil  and  one  part  of  pig's 
lard.  A  mixture  in  the  above  proportions  gives,  when  it 
has  cooled,  a  mass  of  the  most  generally  useful  con- 
sistency. 


270  APPENDIX. 

To  imbed  an  object,  scoop  a  hole  in  a  bit  of  the  paraffin, 
place  the  object  (the  surface  of  which  must  be  dry)  in 
this  hole  and  fill  up  the  latter  with  some  melted  paraffin. 

1 2.  Pasteur's  Solution. 
See  note,  p.  6. 

1 3.  Potash  Solution. 

Dissolve  5  grammes  of  potassic  hydrate  in  100  cubic 
cent,  of  water. 

14.  Schultz's  Solution. 

Dissolve  some  zinc  in  hydrochloric  acid;  permit  the 
solution  to  evaporate,  in  contact  with  metallic  zinc  until 
it  has  attained  a  syrupy  consistence.  Saturate  the  syrup 
with  potassic  iodide,  and  then  add  enough  iodine  to 
make  a  dark  sherry-coloured  solution.  The  object  to  be 
stained  must  be  placed  in  a  little  water,  and  then  some 
of  the  above  solution  added. 

15.  Silver  Nitrate,  Solution  of. 

Dissolve  o'5  grammes  of  silver  nitrate  in  100  cubic 
cent,  of  distilled  water.  Keep  in  an  opaque  stoppered 
bottle. 

1 6.  Sodic  Chloride,  Solution  of.    (Normal  saline  solution. 
Salt  solution?) 

Dissolve  7-5  grammes  of  sodic  chloride  in  i  litre  of  dis- 
tilled water. 


INDEX. 


ABDUCENTES,  nervi,  189 

Acetabulum,  224 

Acrogenous  growth,  47 

Adductor  muscles,  108,  116,  123 

Alse,  84 

Alcoholic  fermentation,  5,  9,  10 

Alga,  48 

Alimentary  canal,  of  Anodonta, 
no,  121 ;  of  Crayfish,  13,1,  148; 
of  Frog,  167,  173,  205;  of  Lob- 
ster, 131,  148;  of  Tadpole,  163 

Alinasal  process,  171 

Alternation  of  generations,  37,  47, 
61 

Ambulatory  limbs,  129,  151 

Amoeba,  17;  Laboratory  wcrk,  2 1 

Amoeboid  movements,  20,  105 

Anacharis,  protoplasmic  move- 
ments in,  54 

Angulo-splenial,  220 

Annulus,  66 

Anodonta  cygncca,  107;  Laboratory 
work,  113 

Antennae,  130,  153 

Antennules,  130,  153 

Anterior  commissure,  186 

Anterior  abdominal  vein,  180, 
200,  234 

Anther,  70,  84 

Antheridium,  43,  45,  51,  60,  68 

Antherozooids,  46,  52,  61,  68 

Aortic  arches,  176,  203,  236 

Appendages,  of  Bean,  70,  78;  of 
Chara,  42,  48;  of  Crayfish,  128, 
142,  151;  of  Frog,  160,  197, 
212;  of  Lobster,  128,  140,  151 

Aqueous  humour,  246 


Arachnoid  membrane,  168 

Archegonia,  61,  68 

Arterial  system,  of  Anodonta,  in; 
of  Crayfish,  133,  145,  149;  of 
Frog,  177,  237;  of  Lobster,  133, 

H5»  H9 

Artery,  cceliac,  178,  cceliaco-me- 
senteric,  178,  237;  cutaneous, 
178;  femoral,  178,  238;  hypo- 
gastric,  178,  238;  iliac,  178,  238; 
lingual,  i77i  237 ;  mesenteric, 
178;  ossophageal,  178;  pulmo- 
cutaneous,  178,  203,  237;  pul- 
monary, 176,  178;  subclavian, 
178;  vertebral,  178 

Articular  process,  213 

Arytenoid  cartilages,  181 

Asci,  36 

Ascospores,  8,  36,  41 

Astacus  fluviatiliS)  127;  Labora- 
tory work,  140 

Astragalus,  225 

Atlas  vertebra,  213 

Atrium,  175,  201 

Auditorii,  nervi,  190 

Auditory  organs,  of  Anodonta,  113, 
121 ;  of  Crayfish,  138,  156;  of 
Frog,  194,  247  j  of  Lobster,  138, 
156 

Axillary  vein,  236 

Axis  cylinder,  257 

B. 

Bacillus,  28 

Bacteria,  25  ;  Laboratory  work,  27 

Balantidium,  93 

Bark,  72 

Basipodite,  151 


INDEX. 


Bast  cells,  65,  73 

Bean  plant,  70 ;  Laboratory  work, 

78 
Bell- Animalcule,  89;   Laboratory 

work,  93 
Blood,     of    Anodonta,     112;     of 

Frog,  174,  210;  of  Lobster,  135 
Blood  corpuscles,  coloured,   211; 

colourless,  20,  23,  112,  135,  174, 

211 

Body  cavity,  of  Hydra,  101,  105 
Bojanus,  organs  of,  117 
Brachial,  plexus,   192;  vein,  179, 

236  ;  nerve,  243 
Bracken    Fern,    55 ;    Laboratory 

work,  62 
Brain,  185,  239 
Branchio-cardiac  veins,  134 
Branchiostegite,  130,  143 
Browspot,  195 

Bud,  terminal,  of  Chara,  42,  50 
Buds,  70 
Byssus,  113,  126 

C. 

CALCANEUM,  225 

Calcar,  169,  225 

Calyx,  70,  83 

Cambium,  72,  80,  8 1 

Campanula  media,  88 

Canalis  centralis,  192,  242 

Carapace,  128,  139 

Carcht'sium,  97 

Carina,  84 

Carotid,    artery,    177,    178,    203, 

237;  gland,  237 
Capitulum,  45 
Carpopodite,  151 
Carpus,  223 

Cartilage,  169,  171,  253 
Cerebellum,'  185,  240 
Cerebral  hemispheres,  185,239 
Cerebro  spinal,  axis,  168;  nervous 

system,  185 
Cephalic  fkxure,  129 
Cephalic  ganglia,  112,  119 
Cephalothorax,  127,  140,  143 
Cervical  groove,  129 


Cervical  suture,  128,  140 

Chara,  42;  Laboratory  work,  48 

Chelae,  129,  152 

Chiasma,  optic,  241 

Chlorophyll,  n,  45,  49,  75,  ico, 
103 

Chondro-cranium,  170 

Choroid,  coat,  247;  plexus,  185 

Cilia,  of  Anodonta,  119;  of  anthero- 
zooids,  46,  52,  61,  68 ;  of  Bell- 
animalcule,  91,  95 ;  of  the  Frog, 
252;  of  Hydra,  99,  105;  of 
Protococcus,  13,  15;  of  Spiril- 
lum volutans,  25 

Circulatory  organs,  of  Anodonta, 
in,  116;  of  Crayfish,  133,  145; 
of  Frog,  174,  201,  234  ;  of  Lob- 
ster, 133,  145 

Clavicle,  222 

Cloaca,  of  Anodonta,  109, 115;  of 
Frog,  167,  206 

Clubmosses,  74,  75 

Cochlea,  194 

Coeliac  artery,  178 

Coeliaco-mesenteric  artery,  1 78, 
237 

Colon,  173 

Columella,  34 

Columella  auris,  194,  217 

Colourless    blood-corpuscles,    20, 

23.  II2»  135,  J74>  211 
Cotyledon,  71,  86 
Conidia,  32,  39 
Conidiophores,  39 
Conifers,  74 
Conjugation,  36,  92,  97 
Connective  rod,  137,  154 
Connective  tissue,  169,  255 
Contractile  vesicle,  18,  21,  91,  94 
Coracoid,  222 
Cornea,  137,  245 
Corolla,  70,  84 
Corpus  adiposum,  198,  204 
Corpuscula,  75 
Cortical  layer,  of  Chara,    42  ;  of 

Bell-animalcule,  94 
Cothurnia,  97 
Coxopodite,  151 
Cranial  nerves,  187 


INDEX. 


273 


Crura  cerebri,  186,  241 
Crural  nerve,  193 
Crystalline  lens,  137,  154,  246 
Cutaneous    glands,    262 ;    artery, 
178 

D. 

DACTYLOPODITE,  151 

Dentary  bone,  220 

Derails,  261 

Development,  of  Anodonta,  112  ; 

of  Bean,  71 ;  of  Chara,  46,  50 ; 

of  Crayfish,  139;  of  Fern,  60; 

of  Frog,  162;  of  Lobster,  139; 

of  Mucor,  34,    37;    of  Penicil- 

lium,  32,  40 
Diaphragm,  166 
Dorsal  aorta,   178,  237 
Dorso-lumbar  vein,  180 
Dotted  ducts,  81 
Duodenum,  173 


E. 

EAR,  see  Auditory  organ 

Ecdysis,  139 

Ectoderm,  100,  103 

Ectosarc,  18,  21 

Embryo,  of  Anodonta,  112-,  126; 

of  Bean,  71,  86;  of  Chara,  47; 

of  Fern,  61 ;  of  Frog,   162 ;  of 

Lobster,  139 
Embryo,  cell  61,  71,  86;  sac,.  71, 

8(5,88 

Encephalon,  185,  239 
Encystation,    of  Amoeba,    19;    of 

Vorticella,  92,  97 
Endoderm,  100,  103 
Endogenous  cell  division,  4 
Endoplast,  92 
Endopodite,  131,  142,  153- 
Endosarc,  21 
Endoskeleton,  169,  211 
Endosperm,  71,  86 
Endosporium,  36 
Epicoracoid,  222 
Epidermis,  of  Bean,   72,   79,    81 ; 

of  Fern,  56,  58,  63;   of  Frog, 

261  '•->. 

M. 


Epithelium,  251 

EpistyliSy  97 

Eustachia"n  recesses,  166,  196,  248 

Evening  Primrose,  87 

Exoccipital,  217 
"  Exogens,  73 

Exopodite,  131,  142,  153 

Exoskeleton,  of  Anodonta,  113, 
124;  of  Crayfish,  127,  140;  of 
Frog,  169;  of  Lobster,  137,  139 

Exosporium,  36 

Eye,  of  Crayfish,  137,  153;  of 
Frog,  194,  244;  of  Lobster, 

W*  «53 

Eyestalks.  130,  153 

F. 

FACIALIS,  nervus,  190 

Femoral  artery,  178,  238;  vein, 
179 

Fenestra  ovalis,  195,  217,  248 

Fermentation,  alcoholic,  i,  5,  9, 
10;  putrefactive,  26 

Fertilization,  process  of,  in  Ano- 
donta, 112;  in  Bean,  7 1 ;  in  Cha- 
ra, 46;  in  Fern,  61 ;  in  Frog, 
162;  in  Hydra,  i QO 

Fibro-vascukr  bundles,  57,  63, 
64,  72,  80 

Fibula,.  225 

Filament,  84 

Filum  terminale,,  wja 

Fission,  92,  96,  9,9 

Flower,  of  Bean,  70,  83 

Fontanelle,  170 

Foot,  of  Anodonta,  107,  115 

Foramen  of  Munro,  1 86 

Foramen  magnum,  2.1 6 

Fourth  ventricle,  185,  240 

Fresh  water,.  Crayfish,  127;  La- 
boratory work,  140 ;  Mussel, 
107 ;  Laboratory  work,  113; 
Polypes,  c,8;  Laboratory  work, 
102 

Frog,  159;  Laboratory  work,  196 

Fronds,  55,  58,  67 

Fungi,  31 

Funiculus,  86 

18 


274 


INDEX. 


G. 

GASTRIC    skeleton    of   Crayfish, 

*3r»  J49 

Gastric  vein,  180,  235 
Gasserian  ganglion,  188,  258 
Gemmation,  4,  u,  15,  92,  99 
Generative  organs,  see  Sexual  or- 
,      gans 

Genito-urinary  canal,  206 
Germinal,  spot,  106,  184,  265 ;  ve- 
sicle, 1 06,  184,  265 
Gills,  of  Crayfish,    136,   144;    of 
Lobster,  136,  144;  of  Tadpole, 
163 

Girdle  bone, '21 8 
Glenoid  fossa,  221 
Glochidium,  112 
Glossopharyngeus,     nervus,     1 90, 

243 

Glottis,  167,  181,  197,  208 
Green  gland,  136,  150 
Gustatory  disks,  251;  organ,  195, 
250 

H. 

HARDERIAN  gland,  194 

Hay  infusion,  28 

Heat  stiffening,  19,  22,  23 

Heart,  of  Anodonta,  in,  116;  of 
Crayfish,  133,  145;  of  Frog, 
175,  201;  of  Lobster,  133,  145 

Histology,  of  Anodonta,  118,  122, 
124;  of  Bean,  72,  79,  82;  ot 
Blood,  23,210;  of  Bracken 
Fern,  56,  63;  of  Chara,  43,  48; 
of  Crayfish,  144,  148,  150,  153, 
155;  of  Frog,  204,  206,  250, 
251;  of  Hydra,  100,  104;  of 
Lobster,  136,  148,  150,  153, 
155;  of  Mucor,  33,  40;  of  Pe- 
nicillium,  31,  38 

Homarus  vulgaris,  127;  Labora- 
tory work,  140 

Humerus,  222 

Humour,  aqueous,  246;  vitreous, 
246 

Hydra  fusca  and  H.  viridis,  98; 
Laboratory  work,  102 


Hyoid  bone,  166,  220 
Hyphse,  31,  34,  38—40 
Hypogastric  artery,  178,  238 
Hypoglossal  nerve,  203,  243 

I. 

ILEUM,  173 

Iliac  arteries,  178,  238;  vein,  179 

Ilium,  224 

Inert  layer,  210 

Infundibulum,  186 

Infusoria,  89 

Innominate  vein,  179,  236 

Integument,  of  Frog,  195,  261 

Inspiration,  182 

Intercellular  passages,  59,  83 

Internal  ear,  194,  248 

Internodes,  42,  48,  55,  62,  70 

Inter- ocular  gland,  195 

Inter- vertebral  foramina,  215 

Intestine,  of  Anodonta,  no,  122; 
of  Crayfish,  132,  148;  of  Frog, 
I67>  I73»  204>  2°5  J  of  Lob- 
ster, 132,  148;  of  Tadpole,  163 

Iris,  245 

Irritability,  muscular,  266 

Ischiopodite,  151 

Ischium,  224 

J- 

JUGULAR  vein,  external,  178,235; 
internal,  178,  236 

K. 

KIDNEYS,  183,  206,  263 


LABIAL  palpi,  108,  115 

Laboratory  work,  Amoeba,  21; 
Anodonta,  113;  Bacteria,  27; 
Bean,  78 ;  Bell-animalcule,  93 ; 
Bracken  Fern,  62;  Chara,  48; 
Crayfish,  140;  Frog,  196;  Hy- 
dra, 102;  Lobster,  140;  Mucor, 
40;  Penicillium,  38;  Protococ- 
cus,  14;  Yeast,  6 


INDEX. 


275 


Labrum,  129 
Labyrinth,  194,  249 
Lamina  terminalis,  186 
Laryngeal  nerve,  191,  243 
Laryngo-tracheal  cartilages,  181 
Larynx,  181,  203,  208 
Lateral  ventricle,  186,  241 
Leaf,  of  Bean,  70,  82 ;  of  Chara, 

49;  of  Fern,  55,  58,  66 
Lens,  crystalline,  246 
Liber,  73,  80,  8r 
Lieno-intestinal  vein,  180,  235 
Limbs,  of  Crayfish,  128,  142,  151; 

of  Frog,   159,  197;  of  Lobster, 

128,  142,  151 
Lingual  artery,  177,  237 
Liver,  of  Anodonta,  no,  122;  of 

Crayfish,    132,    148;    of  Frog, 

174,  201;  of  Lobster,  132,  148 
Lobster,    127;   Laboratory  work, 

140 

Lumbosacral  plexus,  192,  242 
Lung,  182,  208 
Lymph,  174 
Lymph-hearts,  174,  180 
Lymph  sinus,   subvertebral,   165, 

174 

M. 

MANDIBLE,  129,  153,  219 

Mantle,  107,  114 

Manubrium,  45 

Manus,  160,  223 

Maxilla,  of  Crayfish,  129,  152;  of 

Frog,  219 

Maxillipede,  129,  152 
Maxillo-mandibular  nerve,  188 
Meckel's  cartilage,  171,  220 
Medulla,  72,  79;  oblongata,   185, 

240 
Medullary  cavity,    79;    rays,   80; 

sheath,  257 
Membrana    tyrapani,     194,     196, 

247 

Mento-Meckelian  bone,  220 
Meropodjjte,  151 
Mesencephalon,  185,  240 
Mesenteric  artery,  1 78 


Mesentery,  165,  204,  205 
Metacarpal  bones,  223 
Metamorphosis,  113 
Metastoma,  129 
Metatarsal  bones,  225 
Metencephalon,  185,  240 
MicrococcuS)  28 
Micropyle,  71,  86,  112 
Midbrain,  185,  240 
Motor  oculi,  nervus,  187 
Moulds,  30 
Mucor,  30,  34 ;  Laboratory  work, 

40 
Muscle,   histology   of,    124,    150, 

256;  physiology  of,  265 
Muscular  system,    of    Anodonta, 

123;  of  Hydra,    101,    105;  of 

Frog,  226 
Musculo-cutaneous  vein,  179,  199, 

236 

Mycelium,  31,  35,  38 
Myelon,  191,  240 
Myology,  of  the  Frog,  226 

N. 

NARES,  166,  196,  208,  249 
Nasal  bones,  2 1  ^ 
Nematocysts,  100,  104 
Nerve,  cells,  150,  257  j  fibres,  150, 

257 

Nerve,  physiology  of,  265 
Nervous  system,  of  Anodonta,  109, 
112;  of  Crayfish,   136,   149;  of 
Frog,  185,  238;  of  Lobster,  136, 
149 

Nerve,  auditory,  239;  brachial, 
243;  crural,  193;  facial,  190; 
glossopharyngeal,  190,  243 ; 
hypoglossal,  203,  243;  laryn- 
geal,  191,  243;  maxillo-mandi- 
bular,  188,  motor  oculi,  187; 
olfactory,  187,  239 ;  orbito-nasal, 
1 88;  palatine,  188;  pathetic, 
188;  sciatic,  193,  233  ;  trigemi- 
nal,  1 88;  tibial,  193 
Nettle  hair,  protopl.  movt.  in,  54 
Neural,  arch,  212;  canal,  216; 
cavity,  168 


276 


INDEX. 


42,  52 

Node,  42,  48,  55,  62,  70,  78 
Notochord,  169 
Nucleolus,  1 8 

Nucleus,  of  Amoeba,  18,  21;  of 
ovule,  70,  85;  of  Vorticella,  92, 
94 

O.    *..'. 

OBLIQUE  muscles,  194 
Occipital  condyle,  -216 
(Enothera  biennis,  87 
(Esophageal  artery,  1 7 
GEsophagus,    of    Bell-animalcule, 

9°>  935  of  Anodonta,  109,  122; 

of  Crayfish,  131,  148;  of  Frog, 

173,  208 
Olfactory,  lobes,  187,  239;  nerves, 

187,  '239;  organs,   193,  249 
Omosternum,  221 
Opercular  membrane,  163 
Ophthalmites,  130,  153 
Optic,    commissure,    241 ;    lobes, 

185,  240;  nerves,  r87,  241,  245; 

thalami,  186,  239;  tracts,  241 
Orbito-nasal  nerve,  188 
Organ  of  Bojanus,  1 10,  1 1 7 
Os,  cruris,  224;femoris,  224;  pu- 

bis,  224 

Otolith,  121,  194 
Ovary,  of  Anodonta,  112,  123;  of 

Crayfis;h,    147;  of    Frog,    183, 

264;  of  Hydra,    100,    106;   of 

Lobster,  147 

Oviduct,  147,  148,  184,  208 
Ovules,  70,  85 
Ovum,  of  Anodonta,  112,  123;  of 

Crayfish,    139 ;   of   Frog,    184, 

264 ;   of  Hydra,    100,    106 ;  of 

Lobster,  139 

P. 

PALATINE,  bone,  218;  nerve,  188 

Pallium,  1 08,  114 

Pancreas,  174,  205 

Papillae,  filifonnes,  195,  ^50;  fun- 

gifoi'mes,  195,  250 
Parasphenoid  bone,    2 1 8 
Parenchyma,  57,  63, 64,  72,  79,  80 


Parieto-frontal  bone,  2 1 7 
Parieto-splanchnic  ganglion,    112, 

1 20 

Pasteur's  fluid,  6 
Patheticus,  nervus,  188 
Pectoral  arch,  172,  221 
Pedal  ganglion,  112,  120 
Peduncle,  83 
Pelvic  arck,  172,  224 
Pelvic  vein,  179,  234 
Penicillium,  30;  Laboratory  work, 

3.3 
Pericardium,   of   Anodonta,   in, 

116;  of  Crayfish,  133,  145;  of 

Frog,    165,    20 1 ;    of    Lobster, 

133,  H5 
Perilymph,  194 
Peristome,  90,  93 
Periotic  capsule,  171,  217 
Peroneal  nerve,  193,  233 
Pes,  1 60,  225 
Petal,  84 
Petiole,  82 
Phalanges,  223,  225 
Pia  mater,  238 
Pigment-cells,  196,  261 
Pineal  gland,  186,  239 
Pinnule,  55 
Pistil,  70,  84,  85 
Pith,  72,  79 

Pituitary  body,  186,  241 
Pleuroperitoneal      cavity,       165  ; 

membrane,  165,  201 
Plumule,  71,  86 
Pneumogastric  nerve,  191,  243 
Pollen,  70,  85 
Posterior  commissure,  186 
Posterior  tibial  nerve,  233 
Prcecoracoid,  222 
Prsenasal  process,  1 70 
Premaxillary  bone,  217 
Primine,  85 
Primitive  sheath,  257 
Primordial  utricle,  32,  45,  83 
Pro-embryo  of  Chara,  47 
Pro-otic,  217 
Propodite,  151 
Prosencephalon,  186,  239 
Proteus  Animalcule,  17 


INDEX. 


277 


Prothallus,  60,  67 

Protococcus  pluvialiS)  1 1 ;  Labora- 
tory work,  14 

Protoplasmic  movements  in  vege- 
table cells,  45,  52 

Protopodite,  131,  142 

Pseudopodia,  17,  21 

Pteris  aquilina,  55 ;  Laboratory 
work,  62 

Pterygoid  bone,  219 

Pterygoid  rod,  171       ' 

Pulmocutaneous  artery,  176,  203, 

Pulmonary,  artery,  176,  178;  vein, 

175,  180,238 
Putrefaction,  20 
Pylangium,  176 

Q- 

QUADRATE  bone,  219 
Quadrato-jugal  bone,  219 

R. 

RACHIS,  55 

Radicle,  71,  86 

Radius,  223 

Rana  temporaria  and  R.  esculenta, 
159;  Laboratory  work,  196 

Recti  muscles,  194 

Rectum,  of  Anodonta,  no,  122  ; 
of  Crayfish,  133,  148;  of  Frog, 
173,  204  ;  of  Lobster,  13.3,  148 

Renal  veins,  1 79 

Renal  portal  veins/ 2 35,  236 

Respiratory  organs,  of  Anodonta, 
118;  of  Crayfish,  135,  144;  of 
Lobster,  135,  144;  of  Frog,  181 

Restiform  bodies,  185 

Retina,  247,  258 

Retractor  bulbi,  194 

Rhinal  processes,  171 

Rhinencephalon,  239 

Rhizome,  55,  62 

Roots,  of  the  spinal  nerves,  192, 
240 

Rootsheath,  72,  79 
S. 

Saccharomyces  cerevisi(E>  I ;  Labo- 
ratory work,  6 


Sacculus,  194 

Sacrum,  214 

Scalariform  ducts,  58,  65 

Scaphognathite,  128,  153 

Scapular  vein,  179 

Sciatic,   nerve,    193;    vein,    179, 

Sclerenchyma,  57,  63,  64,  65 

Sclerotic,  194,  245 

Secondary  capitula^  45 

Secundine,  $5 

Seed,  71,  86 

Seed-leaves,  71,  86 

Sense  organs,  of  Anodonta,  112, 
12 1 ;  of  Crayfish,  137,  1 53 ;  of 
Frog,  193,  244;  of  Lobster, 

J37,  153 
Sepals,  84 

Septum  nariurn^  170,  249 
Sexual  organs,  of  Anodonta,  112, 

123;  of  Bean,  70,  84;  of  Chara-, 

45,  51;  of  Crayfish,   139,  146; 

of  Fern,  59,  66;  of  Frog,  175, 

198;   of   Hydra,    96,    102;    of 

Lobster,  139,  146 
Shell,  of  Anodonta,  124 
Sinus  venosus,  175,  201 
Siphons,     of    Lamellibranchiata, 

109,  115 
Skeleton,  of  Anodonta,  107,  124; 

of  Crayfish,  127,  139;  of  Frog, 

169,  2ii ;  of  Lobster,  127,  139 
Skull,  216 
Somite,  128,  141 
Sorus,  56,  66 
Spermatozoa,   of  Anodonta,  112; 

of  Crayfish,  147;  of  Frog,  183, 

207;  of  Lobster,  147 
Spinal,  column,  212;  cord,   191, 

240,  242  ;  nerves,  244 
Spinous  process,  213 
Spiral  vessels,  58,  65,  73,  80,  83 
Spirillum  volutans,  25,  29 
SpirocJuzte,  29 
Splanchnic  nerve,  191 
Spleen,  174,  205 
Sporangium,  of  Chara,  43,  46  ;  ot 

Bracken,  56,  66 ;  of  Mucor,  34, 


278 


INDEX. 


Spore,   of   Moulds,    31,    34;    of 

Fern,  56,  66 
Spore  fruit,  43,  46,  51 
Squamosal  bone,  217 
Stamens,  70,  84 
Starch,  45,  57,  64,  81 
Stellate  cells,  82 
Stem,  of  Chara,   42,   48,    79,*    of 

Bracken  (rhizome),  55,  63 
Sternal  artery,  133,  149 
Stigma,  70,  87 
Stipule,  82 
Stomach,  of  Anodonta,  no,  122; 

of  Crayfish,  131,  148;  of  Frog, 

J67,  J73>  2°5J  of  Lobster,  131, 

148 

Stomata,  59,  73,  82,  83 
Stoneworts,  42 
Striated  spindle,  138,  155 
Style,  70,  85 
Subclavian  artery,  1 78 ;  vein,  179, 

235 

Subcesophageal  ganglion,  137 
Sub-vertebral  lymph  sinus,  165 
Supracesophageal  ganglion,    136, 

149 

Suspensonum,  171 
Sympathetic  system,  185,  193,  243 
Synangium,  176 

T. 

TADPOLE,  163 

Tarsus,  225 

Teeth,  of  Frog,  164,  173;  gastric, 
of  Crayfish,  132 

Telson,  140,  142 

Tendo  Achillis,  231 

Tendril,  82 

Tentacles,  98,  102 

Terminal  bud,  of  Chara,  43,  50 ; 
of  Bean,  70,  73 

Terminal  cell,  43,  49,  50 

Testa,  86 

Testis,  of  Anodonta,  112;  of  Cray- 
fish, 146;  of  Frog,  183,  207, 
263;  of  Hydra,  99,  105;  of 
Lobster,  147 

Thalamencephalon,  186,  239 


Thalami  optici,  186,  239 

Third  ventricle,  186,  239 

Thread  cells,  100,  104 

Thymus  gland,  181 

Thyro-hyal,  220 

Thyroid  gland,  181 

Tibia,  225 

Tibial  nerve,  193 

Tongue,  167,  195,  197 

Torula  cerevisitz,   i  ;    Laboratory 

work,  6 

Torula,  of  Mucor,  37 
Tradescantia,  protopl.  movts.  in, 

53 

Transverse  process,  213 
Trigeminal  nerve,  188 
Trachea,  181,  208 
Truncus  arteriosus,  175,  176,  201 
Tympanic  membrane,  194, 247 
Tympanum,  194,  247,  248 

U. 

ULNA,  223 

Umbo,  125 
Unguis,  84 
Unio,  107 
Ureter,  183,  206 
Urinary  bladder,  183,  204 
Urostyle,  170,  214 
Urticating  capsules,  100 
Utriculus,  194 

V. 

VACUOLE,    alimentary,   94;    con- 
tractile,  18;  in  vegetable  cells, 

2,  7,  32,  34,  39,  49 
Vagus  nerve,  191,  243 
Vallisneria,  protopl.  movts.  in, 

54 
Vas  deferens,  of  Crayfish,  146;  of 

Frog,  183,  207;  of  Lobster,  147 
Vascular  bundles,  57,  63,  72,  79 
Vascular  system,  see   Circulatory 

organs 
Vein,  axillary,  236;  brachial,  179, 

236;     branchio-cardiac,      134; 

dorsolumbar,  180;  femoral,  179; 
ric,    180,    235;    iliac,    170  ; 


INDEX. 


279 


innominate,  179,  236 ;  jugular, 
external,  179,  235  ;  jugular,  in- 
ternal, 178,  236;  lieno- intesti- 
nal, 1 80,  235 ;  musculo-cuta- 
neous,  179,  199,  236;  pelvic, 

179,  234;  pulmonary,  175,  180; 
scapular,  179;  sciatic,  179,  235; 
subclavian,  179,  235  ;  renal,  179; 
renal  portal,   235,  236;  portal, 

180,  235 

Vena,  cava,  of  Anodonta,  in,  117; 
of  Frog,  infr.,  178,  236;  of 
Frog,  supr.,  178,  236;  innomi- 
nata,  178,  236;  portse,  180,  235 

Venous  system  of  Frog,  178 

Ventricles  of  the  brain,  185 

Vertebra,  212 

Vertebral  artery,  178 

Vertebral  column,  212 

Veronica  serpyllifolia,  87 

Vesicula  seminalis,  206 

Vestibulum,  90,  93 

Vexillum,  84 

Vibriones,  26,  29 

Viciafaba,)  70;  Laboratory  work, 
78 

Vitelline  membrane,  184,  265 

Vitellus,  1 06,  184,  265 


Vitreous  humour,  246 

Visceral  nervous  system,  of  Cray- 
fish, 136 

Vocal,  sacs,  167;  ligaments,  181 

Vomer,  218 

Vorticellay  89;  Laboratory  work, 
93 

W. 

WHITE  fibrous  tissue,  255 
Wood,  72,  80      . 

X. 

XlPHISTERNUM,  221 

Y. 

YEAST,  i ;  Laboratory  work,  6 
Yelk  division,  Hydra,  100;  Frog, 
162 


ZOOGLOEA,  26,  28 
Zygapophysis,  213 
Zygospore,  36 


PRINTED    BY    C.  J.    CLAY,     M.A, 
AT  THE    UNIVERSITY   PRESS. 


February,  1876. 


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WORKS 
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Snowball.— THE  ELEMENTS  OF  PLANE  AND  SPHERI- 

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Tebay. — ELEMENTARY  MENSURATION  FOR  SCHOOLS. 

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A  TREATISE  ON  THE  INTEGRAL  CALCULUS  AND  ITS 
APPLICATIONS.  With  numerous  Examples.  Fourth  Edition, 
revised  and  enlarged.  Crown  8vo.  cloth,  los.  6d. 

EXAMPLES    OF    ANALYTICAL    GEOMETRY    OF    THREE 

DIMENSIONS.   Third  Edition,  revised.     Crown  8vo.  cloth.    4*. 

A  TREATISE  ON  ANALYTICAL   STATICS.     With  numerous 

Examples.     Fourth  Edition,  revised  and  enlarged.     Crown  8vo. 

cloth,      los.  6d. 

A  HISTORY  OF  THE  MATHEMATICAL  THEORY  OF 
PROBABILITY,  from  the  time  of  Pascal  to  that  of  Laplace. 
8vo.  i8j. 

RESEARCHES  IN  THE  CALCULUS  OF  VARIATIONS, 
principally  on  the  Theory  of  Discontinuous  Solutions  i  an  Essay 
to  which  the  Adams  Prize  was  awarded  in  the  University  of  Cam- 
bridge in  1871.  8vo.  6s. 

A    HISTORY    OF    THE    MATHEMATICAL    THEORIES   OF 
ATTRACTION,   AND  THE   FIGURE   OF   THE   EARTH, 
from  the  time  of  Newton  to  that  of  Laplace.     2  vols.     8vo.      24^. 
"  Such  histories  are  at  present  more  valuable   than   original  work. 
They  at  once  enable  the  Mathematician  to  make  himself  master  of  all  that 
has  been  done  on  the  subject,  and  also  give  him  a  clue  to  the  right  method 
of  dealing  with  the  subject  in  future  by  showing  him  the  paths  by  which 
advance  has  been  made  in  the  past  .  .  .  It  is  with  unminghd  satisfaction 
that  we  see  this  branch  adopted  as  his  special  subject  by  one  whose  cast  oj 
mind  and  self  culture  have  made  him  one  of  the  most  accurate,  as  he  cer- 
tainly is  the  most  learned,  of  Cambridge  Mathematicians" — SATURDAY 
REVIEW. 

AN  ELEMENTARY  TREATISE  ON  LAPLACE'S,  LAME'S, 
AND  BESSEL'S  FUNCTIONS.  Crown  8vo.  los.  6d. 


Wilson  (J.  M.)— ELEMENTARY  GEOMETRY.  Books 
I.  II.  III.  Containing  the  Subjects  of  Euclid's  first  Four  Books. 
New  Edition,  following  the  Syllabus  of  the  Geometrical  Associa- 
tion. By  J.  M.  WILSON,  M  A.,  late  Fellow  of  St.  John's  Col- 


SCIENCE. 


Wilson  (J.  M.)—  continued. 

lege,   Cambridge,  and   Mathematical   Master  of  Rugby   School 
Extra  fcap.  8vo.     3^.  t>d. 

SOLID  GEOMETRY  AND  CONIC    SECTIONS.     With  Appen- 
dices  on  Transversals  and  Harmonic   Division.     For  the  use  of 
Schools.    By  J.  M.  WILSON,  M.A.    Second  Edition.    Extra  fcap 
8vo.     3-r.  6d. 

Wilson  (W.  P.)  — A  TREATISE  ON  DYNAMICS.  By 
W.  P.  WILSON,  M.A.,  Fellow  of  St.  John's  College,  Cambridge, 
and  Professor  of  Mathematics  in  Queen's  College,  Belfast.  8vo. 
9-r.  6d. 

"This  treatise  supplies  a  great  educational  need. "—EDUCATIONAL 

TIMES. 

Wolstenholme.-— A  BOOK  OF  MATHEMATICAL 
PROBLEMS,  on  Subjects  included  hi  the  Cambridge  Course. 
By  JOSEPH  WOLSTENHOLME,  Fellow  of  Christ's  College,  some- 
time Fellow  of  St.  John's  College,  and  lately  Lecturer  in  Mathe- 
matics at  Christ's  College.  Crown  8vo.  cloth.  8j.  6d. 
"  Judicious,  symmetrical,  and  well  arranged"—  GUARDIAN. 


SCIENCE. 

ELEMENTARY   CLASS-BOOKS. 

IT  is  the  intention  of  the  Publishers  to  produce  a  com- 
plete series  of  Scientific  Manuals,  affording  full  and  ac- 
curate elementary  information,  conveyed  in  clear  and 
lucid  English.  The  authors  are  well  known  as  among 
the  foremost  men  of  their  several  departments ;  and  their 
names  form  a  ready  guarantee  for  the  high  character  of  the 
books.  Subjoined  is  a  list  of  those  Manuals  that  have 
already  appeared,  with  a  short  account  of  each.  Others 
are  in  active  preparation ;  and  the  whole  will  constitute  a 
standard  series  specially  adapted  to  the  requirements  of  be- 
ginners, whether  for  private  study  or  for  school  instruction. 
ASTRONOMY,  by  the  Astronomer  Royal. 

POPULAR  ASTRONOMY.  With  Illustrations.  By  SIR  G.  B. 
AIRY,  K.C.B.,  Astronomer  Royal.  New  Edition.  l8mo. 
cloth,  4J.  6ct. 

Six  lectures,  intended  "to  explain  to  intelligent  persons  the  principles 
on  which  the  instruments  of  an   Observatory  are  constructed,  and  the 


16  EDUCATIONAL  BOOKS. 

Elementary  Class- Books — continued. 

principles  on  -which  the  observations  made  with  these  instruments  are 
treated  for  deduction  of  the  distances  and  weights  of  the  bodies  of  the 
Solar  System" 

ASTRONOMY. 

ELEMENTARY  LESSONS  IN  ASTRONOMY.  With 
Coloured  Diagram  of  the  Spectra  of  the  Sun,  Stars,  and 
Nebulae,  and  numerous  Illustrations.  By  J.  NORMAN  LOCKYER, 
F.R.S.  New  Edition.  i8mo.  $s.  6d. 

"  Fully  clear >  sound ,  and  worthy  of  attention ,  not  only  as  a  popular  expo- 
sition, but  as  a  scientific  'Index'" — ATHEN^UM.     "  The  most  fasci- 
nating of  elementary  books  on  the  Sciences" — NONCONFORMIST. 
QUESTIONS    ON    LOCKYER'S    ELEMENTARY    LESSONS 
IN  ASTRONOMY.    For  the  Use  of  Schools.    By  JOHN  FORBES- 
ROBERTSON.     i8mo.  cloth  limp.     is.  6d. 

PHYSIOLOGY. 

LESSONS     IN     ELEMENTARY     PHYSIOLOGY.        With 
numerous  Illustrations.       By  T.  H.  HUXLEY,  F.R.S.,  Professor 
of  Natural  History  in  the  Royal  School  of  Mines.     New  Edition. 
i8mo.  cloth.     4^.  6d. 
* '  Pure  gold  throughout. " — GUARDIAN.     ' '  Unquestionably  the  clearest 

and  most  complete  elementary  treatise  on  this  subiect  that  we  possess  in 

any  language" — WESTMINSTER  REVIEW. 

QUESTIONS  ON  HUXLEY'S  PHYSIOLOGY  FOR  SCHOOLS. 
By  T.  ALCOCK,  M.D.     i8mo.     is.  6d. 

BOTANY. 

LESSONS  IN  ELEMENTARY  BOTANY.  By  D.  OLIVER, 
F.  R.  S. ,  F. L.  S. ,  Professor  of  Botany  in  University  College,  London. 
With  nearly  Two  Hundred  Illustrations.  New  Edition.  i8mo. 
cloth.  4^.  6d. 

CHEMISTRY. 

LESSONS  IN  ELEMENTARY  CHEMISTRY,  INORGANIC 
AND  ORGANIC.     By  HENRY  E.  ROSCOE,  F.R.S.,  Professor  of 
Chemistry  in  Owens  College,  Manchester.     With  numerous  Illus- 
trations and  Chromo-Litho  of  the  Solar  Spectrum,  and  of  the  Al- 
kalies and  Alkaline  Earths.     New  Edition.     i8mo.  cloth.    4^.  6d. 
"  As  a  standard  general  text-book  it  deserves  to  take  a  leading  place." — 
SPECTATOR.     "  We  unhesitatingly  pronounce  it  the  best  of  all  our 
elementary  treatises  on  Chemistry.  "—MEDICAL  TIMES. 
A  SERIES  OF  CHEMICAL  PROBLEMS,  prepared  with  Special 
Reference  to  the  above,  by  T.   E.  THORPE,   Ph.D.,  Professor  of 
Chemistry  in  the  Yorkshire  College  of  Science,  Leeds.    Adapted  for 
the  preparation  of    Students  for  the  Government,    Science,    and 
Society  of  Arts  Examinations.       With    a  Preface  by    Professor 
ROSCOE.     i8mo.      is.     Key.    is. 


SCIENCE.  I7 


Elementary  Class- Books — continued. 

POLITICAL   ECONOMY. 

POLITICAL  ECONOMY  FOR  BEGINNERS.  By  MILLICENT 
G.  FAWCETT.     New  Edition.     i8mo.     2s.  6d. 
"  Clear,  compact,  and  comprehensive." — DAILY  NEWS.   "  The  relations 
of  capital  and  labour  have  never  been   more  simply  or  more  clearly 
expounded"—  CONTEMPORARY  REVIEW. 

LOGIC. 

ELEMENTARY  LESSONS  IN  LOGIC  ;  Deductive  and  Indue- 
tive,  with  copious  Questions  and  Examples,  and  a  Vocabulary  o/ 
Logical  Terms.  By  W.  STANLEY  JEVONS,  M.  A. ,  Professor  of  Logic 
in  Owens  College,  Manchester.  New  Edition.  i8mo.  3^.  6d. 

tl  Nothing  can  be  better  for  a  school-book" — GUARDIAN. 

"  A  manual  alike  simple,  interesting,  and  scientific." — ATHENAEUM. 

PHYSICS. 

LESSONS  IN  ELEMENTARY  PHYSICS.  By  BALFOUR 
STEWART,  F.R.S.,  Professor  of  Natural  Philosophy  in  Owens 
College,  Manchester.  With  numerous  Illustrations  and  Chromo- 
liths  of  the  Spectra  of  the  Sun,  Stars,  and  Nebulae.  New  Edition. 
i8mo.  4-r.  6d. 
.  "  The  beau-ideal  of  a  scientific  text-book,  clear,  accurate,  and  thorough." 

EDUCATIONAL  TIMES. 

. 

PRACTICAL     CHEMISTRY. 

THE  OWENS  COLLEGE  JUNIOR  COURSE  OF  PRAC- 
TICAL  CHEMISTRY.  By  FRANCIS  JONES,  Chemical  Master 
in  the  Grammar  School,  Manchester.  With  Preface  by  Professor 
ROSCOE.  With  Illustrations.  New  Edition.  i8mo.  2s.  6d. 

ANATOMY. 

LESSONS  IN  ELEMENTARY  ANATOMY.    By  ST.  GEORGE 
MIVART,  F.R.S.,  Lecturer  in  Comparative  Anatomy  at  St,  Mary's 
Hospital.    With  upwards  of  400  Illustrations.     i8mo.  6s.  6d. 
11  It  may  be  questioned  whether  any  other  work  on  Anatomy  contains 
in  like  compass  so  proportionately  great  a  mass  of  information. " — LANCET. 
"  The  work  is  excellent,  and  should  be  in  the  hands  of  every  student  of 
human  anatomy" — MEDICAL  TIMES. 

STEAM. — AN  ELEMENTARY  TREATISE.  By  JOHN  PERRY, 
Bachelor  of  Engineering,  Whitworth  Scholar,  etc.,  late  Lecturer  in 
Physics  at  Clifton  College.  With  numerous  Woodcuts  and 
Numerical  Examples  and  Exercises.  i8mo.  4J.  6d. 

B 


1 8  EDUCATIONAL  BOOKS. 

MANUALS    FOR    STUDENTS. 
Flower  (W.  H.)— AN  INTRODUCTION  TO  THE  OSTE- 

OLOGY  OF  THE  MAMMALIA.  Being  the  substance  of 
the  Course  of  Lectures  delivered  at  the  Royal  College  of  Surgeons 
of  England  in  1870.  By  W.  H.  FLOWER,  F.R.S.,  F.R.C.S., 
Hunterian  Professor  of  Comparative  Anatomy  and  Physiology, 
With  numerous  Illustrations  Globe  8vo.  7-r.  6d. 

Hooker   (Dr.)— THE   STUDENT'S   FLORA   OF   THE 

BRITISH  ISLANDS.  By  J.  D.  HOOKER,  C.B.,  F.R.S., 
M.D.,  D.C.L.,  President  of  the  Royal  Society.  Globe  8vo. 
IOJ.  6d. 

"  Cannot  fail  to  perfectly  fulfil  the  purpose  for  which  it  is  intended" — 
LAND  AND  WATER. — "  Containing  the  fullest  and  most  accurate 
manual  of  the  kind  that  has  yet  appeared" — PALL  MALL  GAZETTE. 

Oliver  (Professor). — FIRST  BOOK  OF  INDIAN  BOTANY. 

By  DANIEL  OLIVER,  F.R.S.,  F.L.S.,  Keeper  of  the  Herbarium 
and  Library  of  the  Royal  Gardens,  Kew,  and  Professor  of  Botany 
in  University  College,  London.  With  numerous  Illustrations. 
Extra  fcap.  8vo.  6s.  6d. 

"  It  contains  a  well-digested  summary  of  all  essential  knowledge  pertain- 
ing to  Indian  botany,  wrought  out  in  accordance  with  the  best  principles 
of  scientific  arrangement" — ALLEN'S  INDIAN  MAIL. 

Other  volumes  of  these  Manttals  will  follow. 


NATURE  SERIES. 

THE    SPECTROSCOPE   AND    ITS   APPLICATIONS.      By  J. 

NORMAN  LOCKYER,  F.R.S.     With  Coloured  Plate  and  numerous 

illustrations.     Second  Edition.     Crown  8vo.     $s.  6d. 
THE  ORIGIN  AND   METAMORPHOSES   OF   INSECTS.     By 

SIR  JOHN  LUBBOCK,  M.P.,  F.R.S.     With  numerous  Illustrations. 

Second  Edition.     Crown  8vo.  3-r.  6d. 
"  We  can  most  cordially  recommend  it  to  young  naturalists" — ATHE- 

N^EUM. 

THE  BIRTH  OF  CHEMISTRY.     By  G.  F.  RODWELL,  F.R.A.S., 
F.C.S.,  Science  Master  in  Marlborough  College.     With  numerous 
Illustrations.     Crown  8vo.     3*.  6d. 
"  We  can  cordially  recommend  it    to  all  Students  of  Chemistry"— 

CHEMICAL  NEWS. 

THE  TRANSIT  OF  VENUS.  By  G.  FORBES,  M.A.,  Professor  of 
Natural  Philosophy  in  the  Andersonian  University,  Glasgow. 
Illustrated.  Crown  8vo.  3*.  bd. 

THE  COMMON  FROG.  By  ST.  GEORGE  MIVART,  F.R.S.,  Lec- 
turer in  Comparative  Anatomy  at  St.  Mary's  Hospital.  With 
numerous  Illustrations.  Crown  8vo.  3^.  6d. 


SCIENCE.  I9 


Nature  Series— continued. 

POLARISATION  OF  LIGHT.  By  W.  SPOTTISWOODE,  F.R.S. 
With  many  Illustrations.  Crown  8vo.  3^.  6d. 

ON  BRITISH  WILD  FLOWERS  CONSIDERED  IN  RELA- 
TION TO  INSECTS.  By  SIR  JOHN  LUBBOCK,  Bart.,  F.R.S. 
With  numerous  Illustrations.  Second  Edition.  Crown  8vo.  4^.  6d. 
Other  volumes  to  follow. 

Ball  (R.  S.,  A.M.)— EXPERIMENTAL  MECHANICS. 
A  Course  of  Lectures  delivered  at  the  Royal  College  of  Science 
for  Ireland.  By  R.  S.  BALL,  A.M.,  Professor  of  Applied 
Mathematics  and  Mechanics  in  the  Royal  College  of  Science 
for  Ireland.  Royal  8vo.  i6s. 

Blanford. — THE  RUDIMENTS  OF  PHYSICAL  GEO- 
GRAPHY FOR  THE  USE  OF  INDIAN  SCHOOLS  ;  with  a 
Glossary  of  Technical  Terms  employed.  By  H.  F.  BLANFORD, 
F.R.S.  Fhth  edition,  with  Illustrations.  Globe  8vo.  2s.  6d. 

Gordon. — AN   ELEMENTARY  BOOK   ON  HEAT.      By 

J.  E.  H.  GORDON,  B.A.,  Gonville  and  Caius  College,  Cambridge. 
Crown  8vo.     2s. 

Huxley  &  Martin. — A  COURSE  OF  PRACTICAL  IN- 
STRUCTION IN  ELEMENTARY  BIOLOGY.  By  Professor 
HUXLEY,  F.R.S.,  assisted  by  H.  N.  MARTIN,  M.B.,  D.Sc.  Crown 
8vo.  6s. 

SCIENCE  PRIMERS  FOR  ELEMENTARY 
SCHOOLS. 

In  these  Primers  the  authors  have  aimed,  not  so  much  to  give  informa- 
tion^ as  to  endeavour  to  discipline  the  mind  in  a  way  which  has  not 
hitherto  been  customary,  by  bringing  it  into  immediate  contact  with 
Nature  herself.  For  this  purpose  a  series  of  simple  experiments  (to  be 
performed  by  the  teacher]  has  been  devised,  leading  up  to  the  chief  truths 
of  each  Science.  Thus  the  power  of  observation  in  the  pupils  will  be 
awakened  and  strengthened.  Each  Manual  is  copiously  illustrated,  and 
appended  are  lists  of  all  the  necessary  apparatus,  with  prices,  and 
directions  as  to  how  they  may  be  obtained.  Professor  Huxley's  introduc- 
tory volume  has  been  delayed  through  the  illness  of  the  author,  but  it  is 
now  expected  to  appear  very  shortly.  "  They  are  ivonderfully  clear  and 
lucid  in  their  instruction,  simple  in  style,  and  admirable  in  plan."— 
EDUCATIONAL  TIMES. 

PRIMER  OF  CHEMISTRY.  By  H.  E.  ROSCOE,  Professor  of 
Chemistry  in  Owens  College,  Manchester.  With  numerous  Illus- 
trations. i8mo.  is.  New  Edition. 

PRIMER  OF  PHYSICS.  By  BALFOUR  STEWART,  Professor  of 
Natural  Philosophy  in  Owens  College,  Manchester.  With 
numerous  Illustrations.  l8mo.  is.  New  Edition. 

B    2 


20  EDUCATIONAL  BOOKS. 


PRIMER  OF  PHYSICAL  GEOGRAPHY.  By  ARCHIBALD 
GEIKIE,  F.  R.  S.,  Murchison- Professor  of  Geology  and  Mineralogy 
at  Edinburgh.  With  numerous  Illustrations.  New  Edition. 
i8mo.  is. 

PRIMER  OF  GEOLOGY.  By  PROFESSOR  GEIKIE,  F.R.S.  With 
numerous  Illustrations.  New  Edition.  i8mo.  cloth,  is. 

PRIMER  OF  PHYSIOLOGY.  By  MICHAEL  FOSTER,  M.D., 
F.R.S.  With  numerous  Illustrations.  New  Edition.  i8mo.  is. 

PRIMER  OF  ASTRONOMY.  ByJ.  NORMAN  LOCKYER,  F.R.S. 
With  numerous  Illustrations.  New  Edition.  i8mo.  is. 

PRIMER  OF  BOTANY.  By  J.  D.  HOOKER,  C.B.  F.R.S.,  Presi- 
dent of  the  Royal  Society.  With  numerous  Illustrations.  i8mo. 
is. 

In  preparation : — 
INTRODUCTORY.     By  PROFESSOR  HUXLEY.     &c.  &c. 


MISCELLANEOUS. 

Abbott.— A  SHAKESPEARIAN  GRAMMAR.  An  Attempt  to 
illustrate  some  of  the  Differences  between  Elizabethan  and  Modern 
English.  By  the  Rev.  E.  A.  ABBOTT,  M.A.,  Head  Master  of  the 
City  of  London  School.  For  the  Use  of  Schools.  New  and 
Enlarged  Edition.  Extra  fcap.  8vo.  6s. 

"A  critical  inquiry,  conducted  with  great  skill  and  knowledge,  and 
with  all  the  appliances  of  modern  philology ....  " — PALL  MALL 
GAZETTE.  "  Valuable  not  only  as  an  aid  to  the  critical  study  of 
Shakespeare,  but  as  tending  to  familiarize  the  reader  with  Elizabethan 
English  in  general." — ATHENAEUM. 

Baldwin. — INTRODUCTION  TO  PRACTICAL  FARMING 

FOR  THE  USE  OF  SCHOOLS.  By  T.  BALDWIN,  M.R.I. A. 
Superintendent  of  the  Agricultural  Department  of  National  Educa- 
tion in  Ireland.  i8mo.  is.  6d. 

Barker. — FIRST    LESSONS  IN  THE  PRINCIPLES    OF 

COOKING.  By  LADY  BARKER,  i8mo.  is. 
"  An  unpretending  but  invaluable  little  work  ....  The  plan  is 
admirable  in  its  completeness  and  simplicity  ;  it  is  hardly  possible  that 
anyone  who  can  read  at  all  can  fail  to  understand  the  practical  lessons  on 
bread  and  beef,  fish  and  vegetables  ;  while  the  explanation  of  the  chemical 
composition  of  our  food  must  be  intelligible  to  all  who  possess  sufficient 
education  to  follow  the  argument,  in  which  the  fewest  possible  technical 
terms  are  used" — SPECTATOR. 


MISCELLANEO  US.  2 1 

Berners. — FIRST  LESSONS  ON  HEALTH.    By  j.  BER- 

NERS.     i8mo.      is.     Fourth  Edition. 

Besant. — STUDIES  IN  EARLY  FRENCH  POETRY.    By 

WALTER  BESANT,  M.A.     Crown  8vo.     8s.  6d. 
"  In  one  moderately  sized  volume  he  has  contrived  to  introduce  us  to  the 
very  best,  if  not  to  all  of  the  early  French  poets." — ATHENAEUM. 

Breymann. — Works  by  HERMANN  BREYMANN,  Ph.D.,  late 
Lecturer  on  French  Language  and  Literature  at  Owens  College, 
Manchester,  and  now  Professor  of  Philology  in  the  University  of 
Munich. 

A     FRENCH     GRAMMAR    BASED     ON     PHILOLOGICAL 

PRINCIPLES.  Second  Edition.  Extra  fcap.  8vo.  4*.  6d. 
"  We  dismiss  the  work  -with  every  expression  of  satisfaction.  It  can- 
not fail  to  be  taken  into  use  by  all  schools  which  endeavour  to  make  the 
study  of  French  a  means  towards  the  higher  culture" — EDUCATIONAL 
TIMES.  *^  A  good,  sound,  valuable  philological  grammar.  The  author 
presents  the  pupil  by  his  method  and  by  detail,  with  an  enormous  amount 
of  information  about  French  not  usually  to  be  found  in  grammars,  and 
the  information  is  all  of  it  of  real  practical  value  to  the  student  who 
really  wants  to  know  French  well,  and  to  understand  its  spirit" — 
SCHOOL  BOARD  CHRONICLE. 

FIRST  FRENCH  EXERCISE  BOOK.     Extra  fcap.  8vo.    4?.  6d. 
SECOND  FRENCH  EXERCISE  BOOK.     Extra  fcap.  8vo,     2s.  6d. 

CalderwOOd.— HANDBOOK  OF  MORAL  PHILOSOPHY. 

By  the  Rev.  HENRY  CALDERWOOD,  LL.D.,  Professor  of  Moral 

Philosophy,  University  of  Edinburgh.     Fourth  Edition.     Crown 

8vo.     6s. 

"  A  compact  and  useful  work  ....  will  be  an  assistance  to  many 

students  outside  the  author 's  own  University" — GUARDIAN. 

Delamotte.— A  BEGINNER'S  DRAWING  BOOK.  By  P.  H. 

DELAMOTTE,    F.S.A.      Progressively  arranged.      New  Edition, 
improved.     Crown  8vo.     3-r.  6d. 
('A  concise,  simple,   and  thoroughly  practical  work" — GUARDIAN. 

Fawcett. — TALES  IN  POLITICAL  ECONOMY.    By  MILLI- 

CENT  GARRETT  FAWCETT.     Globe  8vo.  3-r. 

"  The  idea  is  a  good  one,  and  it  is  quite  wonderful  what  a  mass^  of 
economic  teaching  the  author  manages  to  compress  into  a  small  space.  — 
ATHEN^UM. 

Goldsmith. — THE  TRAVELLER,  or  a  Prospect  of  Society  j 
and  THE  DESERTED  VILLAGE.  By  OLIVER  GOLDSMITH. 
With  Notes  Philological  and  Explanatory,  by  J.  W.  HALES,  M.A. 
Crown  8vo.  6d. 


22  EDUCATIONAL  BOOKS. 

Hales. — LONGER  ENGLISH  POEMS,  with  Notes,  Philological 
and  Explanatory,  and  an  Introduction  on  the  Teaching  of  English. 
Chiefly  for  use  in  Schools.  Edited  by  J.  W.  HALES,  M.A., 
Lecturer  in  English  Literature  and  Classical  Composition  at  King's 
College  School,  London,  &c.  &c.  Third  Edition.  Extra  fcap. 
8vo.  4f.  6d. 
' '  The  notes  are  very  full  and  good,  and  the  book,  edited  by  one  of  our 

most  cultivated  English  scholars,  is  probably  the  best  volume  of  selections 

ever  made  for  the  use  of  English  schools" — PROFESSOR  MORT.F.Y'S  First 

Sketch  of  English  Literature. 

Helfenstein  (James). — A   COMPARATIVE   GRAMMAR 

OF  THE  TEUTONIC  LANGUAGES.  By  JAMES  HELFEN- 
STEIN, Ph.D.  8vo.  iSs. 

Hole.— A  GENEALOGICAL  STEMMA  OF  THE  KINGS  OF 
ENGLAND  AND  FRANCE.  By  the  Rev.  C.  HOLE.  On 
Sheet,  is. 

Jephson. — SHAKESPEARE'S  "TEMPEST."  with  Giossanai 

and  Explanatory  Notes.     By  the  Rev.  J.  M.  JEPHSON.     Second 
Edition.     i8mo.     is. 
Literature  Primers. — Edited  by   JOHN    RICHARD    GREEN. 

Author  of  "A  Short  History  of  the  English  People." 
ENGLISH  GRAMMAR.     By  the  Rev.  R.  MORRIS,  LL.D.,  Presi- 
dent of  the  Philological  Society.     i8mo.  cloth,     ij. 
"A   work  quite  precious  in   its   way.  .  .   .  An   excellent   English 
Grammar  for  the  lowest  form." — EDUCATIONAL  TIMES. 
THE      CHILDREN'S      TREASURY     OF     ENGLISH    SONG. 
Selected  and  arranged  with  Notes  by  FRANCIS  TURNER  PALGRAVE. 
In  Two  Parts.      i8mo.      is.  each. 

ENGLISH  LITERATURE.  By  the  Rev.  STOPFORD  BROOKE,  M.A. 
l8mo.     is. 
In  preparation  : — 

LATIN  LITERATURE.  By  the  Rev.  Dr.  FARRAR,  F.R.S. 
GREEK  LITERATURE.     By  PROFESSOR  JEBB,  M.A. 
SHAKSPERE.     By  PROFESSOR  DOWDHN. 
PHILOLOGY.    By  J.  PEILE,  M.A. 
BIBLE  PRIMER.     By  G.  GROVE,  D.C.L. 
CHAUCER.     By  F.  J.  FURNIVALL,  M.A. 
GREEK  ANTIQUITIES.  By  the  Rev.  J.  P.  MAHAFFY,M.A. 
Martin.— THE  POET'S  HOUR :  Poetry  Selected  and  Arranged  for 
Children.  By  FRANCES  MARTIN.  Second  Edition.    i8mo.  2s.  6d. 
SPRING-TIME  WITH  THE  POETS.    Poetry  selected  by  FRANCES 

MARTIN.     Second  Edition.     i8mo.     3*.  6d. 
Masson  (Gustave).— A  COMPENDIOUS  DICTIONARY 

OF  THE  FRENCH  LANGUAGE  (French- English  and  English- 
French).  Followed  by  a  List  of  the  Principal  Diverging  Deriva- 
tions, and  preceded  by  Chronological  and  Historical  Tables.  By 
GUSTAVE  MASSON,  Assistant-Master  and  Librarian,  Harrow 
School.  Second  Edition.  Square  half-bound,  6s. 


MISCELLANEOUS.  23 

"  By  many  degrees  the  most  useful  Dictionary  that  the  student  can 
obtain" — EDUCATIONAL  TIMES. 

"A  book  which  any  student,  whatever  may  be  the  degree  of  his  ad- 
vancement in   the  language,  would  do  well  to  have  on  the  table  close  at 
hand  while  he  is  reading." — SATURDAY  REVIEW. 
Morris. — Works  by  the  Rev.    R.   MORRIS,  LL.D.,  Lecturer  on 

English  Language  and  Literature  in  King's  College  School. 
HISTORICAL     OUTLINES     OF     ENGLISH     ACCIDENCE, 

comprising  Chapters  on  the   History  and    Development  of    the 

Language,  and  on  Word-formation.     Third  Edition.     Extra  fcap. 

8vo.     6s. 

"  It  makes  an  era  in  the  study  of  the  English  tongue" — SATURDAY 
REVIEW.     "  A  genuine  and  sound  book. " — ATHENAEUM. 
ELEMENTARY     LESSONS     IN     HISTORICAL     ENGLISH 

GRAMMAR,  Containing  Accidence  and  Word-formation.  Second 

Edition.     i8mo.     2s.  6d. 
PRIMER  OF  ENGLISH  GRAMMAR.     i8mo.     u. 

Oliphant. — THE  SOURCES  OF  STANDARD  ENGLISH. 

By  J.  KINGTON  OLIPHANT.  Extra  fcap.  8vo.  6s, 
"  Mr.  Oliphant' 's  book  is,  to  our  mind,  one  of  the  ablest  and  most 
scholarly  contributions  -to  our  standard  English  we  have  seen  for  many 
years.  .  .  .  The  arrangement  of  the  work  and  its  indices  make  it  in- 
valuable as  a  work  of  reference,  and  easy  alike  to  study  and  to  store,  when 
studied,  in  the  memory" — SCHOOL  BOARD  CHRONICLE.  "  Comes 
nearer  to  a  history  of  the  English  language  than  anything  that  we  have 
seen  since  such  a  history  could  be  written  without  confusion  and  con- 
tradictions"— SATURDAY  REVIEW. 

Opp'en. — FRENCH    READER.     For  the   Use  of  Colleges  and 

Schools.     Containing  a  graduated  Selection  from  modern  Authors 

in  Prose  and  Verse ;  and  copious  Notes,  chiefly  Etymological.    By 

EDWARD  A.  OPPEN.     Fcap.  8vo.  cloth.    4^.  6d. 

Otte. — SCANDINAVIAN  HISTORY.     By  E.  C.  OTTE.    With 

Maps.     Globe  8vo.  6s. 

"A    readable,    well-arranged,   complete,    and    accurate  volume.  — 
LITERARY  REVIEW. 

Palgrave.— THE  CHILDREN'S  TREASURY  OF  ENGLISH 

SONG.  Selected  and  Arranged  with  Notes  by  FRANCIS  TURNER 
PALGRAVE.  In  Two  Parts.     i8mo.     is.  each. 
"  While  indeed  a  treasure  Jor  intelligent  children,  it  is  also  a  work 

which  many  older  folk  will  be  glad  to  have."— SATURDAY  REVIEW. 

Pylodet.—  NEW  GUIDE  TO  GERMAN  CONVERSATION: 
containing  an  Alphabetical  List  of  nearly  800  Familiar  Words 
followed  by  Exercises,  Vocabulary  of  Words  in  frequent  use, 
Familiar  Phrases  and  Dialogues;  a  Sketch  of  German  Literature, 
Idiomatic  Expressions,  &c.  By  L.  PYLODET.  i8mo,  cloth  limp. 
zs.  6d. 


24  EDUCATIONAL  BOOKS. 


Reading   Books.—  Adapted  to  the  English  and  Scotch  Codes  for 
1875.     Bound  in  Cloth. 

PRIMER.     i8mo.     (48pp.)     2d. 


BO< 

3K      I.  for  Sta 
II. 
III. 
IV. 
V. 
VI. 

ndard      I. 
II. 
III. 
IV. 
V. 
VI. 

i8tno.       (96pp.) 
i8mo.     (144  pp.) 
i8mo.     (160  pp.) 
i8mo.     (176  pp.) 
i8mo.     (380  pp.) 
Crown  8vo.     (43* 

is. 
pp.)      2S. 

Book  VI.   is  fitted  for  higher  Classes,  and  as  an  Introduction  to 
English  Literature. 

Sonnenschein  and  Meiklejohn.  —  THE  ENGLISH 
METHOD  OF  TEACHING  TO  READ.  By  A.  SONNENSCHEIN 
and  J.  M.  D.  MEIKLEJOHN,  M.A.  Fcap.  8vo. 

COMPRISING  : 

THE  NURSERY  BOOK,  containing  all  the  Two-Letter  Words  in 
the  Language,      id,      (Also  in   Large  Type  on  Sheets  for 
School  Walls.     5*.) 
THE  FIRST  COURSE,  consisting  of   Short  Vowels  with  Single 

Consonants.     3^. 
THE  SECOND   COURSE,  with  Combinations    and   Bridges,   con- 

sisting of  Short  Vowels  with  Double  Consonants.     40. 
THE    THIRD    AND    FOURTH     COURSES,    consisting    of   Long 

Vowels,  and  all  the  Double  Vowels  in  the  Language.    6d. 
"  These  are  admirable  books,  because  they  are  constructed  on  a  principle, 
and  that  the  simplest  principle  on  which  it  is  possible  to  learn  to  read 
English"  —  SPECTATOR. 

Taylor.  —  WORDS    AND     PLACES  ;    or,    Etymological    Illus- 

trations of  History,   Ethnology,  and   Geography.     By  the  Rev. 

ISAAC  TAYLOR,  M.A.     Third  and  cheaper  Edition,  revised  and 

compressed.    With  Maps.     Globe  8vo.     6s. 

Already  been  adopted  by  many  teachers,  and  prescribed  as  a  text-book  in 

the  Cambridge  Higher  Examinations  for  Women. 

Thring.  —  Works  by  EDWARD  THRING,  M.A.,  Head  Master  of 
Uppingham. 

THE  ELEMENTS  OF  GRAMMAR  TAUGHT  IN  ENGLISH, 
with  Questions.  Fourth  Edition.  i8mo.  2s. 

THE  CHILD'S  GRAMMAR.  Being  the  Substance  of  "The 
Elements  of  Grammar  taught  in  English,"  adapted  for  the  Use  of 
Junior  Classes.  A  New  Edition.  i8mo.  is. 

SCHOOL  SONGS.  A  Collection  01  Songs  for  Schools.  With  the 
Music  arranged  for  four  Voices.  Edited  by  the  Rev.  E.  THRING 
and  H.  RICCIUS.  Folio.  7*.  6d. 


HISTORY.  25 


Trench  (Archbishop).— Works  by  R.   C.  TRENCH,  D.D., 

Archbishop  of  Dublin. 
HOUSEHOLD  BOOK  OF  ENGLISH    POETRY.     Selected  and 

Arranged,  with  Notes.    Extra  fcap.  8vo.     5^.  6d.  Second  Edition. 
"  The  Archbishop  has  conferred  in  this  delightful  volume  an  import- 
ant gift  on  the  whole  English-speaking  population  of  the  world." — PALL 
MALL  GAZETTE. 
ON  THE  STUDY   OF  WORDS.    Lectures  addressed  (originally) 

to    the   Pupils  at    the    Diocesan  Training  School,   Winchester. 

Fifteenth  Edition,  revised.    Fcap.  8vo.      4^.  6d. 
ENGLISH,   PAST    AND   PRESENT.       Ninth    Edition,    revised 

and  improved.     Fcap.  8vo.     $s. 
A  SELECT  GLOSSARY  OF  ENGLISH  WORDS,  used  formerly 

in  Senses  Different  from  their  Present.     Fourth  Edition,  enlarged. 

Fcap.  8vo.     4J.  6d. 

Vaughan  (C.  M.)— A  SHILLING  BOOK  OF  WORDS 

FROM  THE  POETS.     By  C.  M.  VAUGHAN.     i8mo.  cloth. 

Whitney. — Works  by  WILLIAM  D.  WHITNEY,  Professor  of  San- 
skrit and  Instructor  in  Modern  Languages  in  Yale  College  ;  first 
President  of  the  American  Philological  Association,  and  hon. 
member  of  the  Royal  Asiatic  Society  of  Great  Britain  and  Ireland  ; 
and  Correspondent  of  the  Berlin  Academy  of  Sciences. 

A  COMPENDIOUS  GERMAN  GRAMMAR.     Crown  8vo.     6s. 

A  GERMAN  READER  IN  PROSE  AND  VERSE,  with  Notes  and 
Vocabulary.  Crown  8vo.  Js.  6d. 

Yonge   (Charlotte    M.) — THE  ABRIDGED  BOOK  OF 

GOLDEN  DEEDS.  A  Reading  Book  for  Schools  and  General 
Readers.  By  the  Author  of  "The  Heir  of  Redclyffe."  i8mo. 
cloth.  is. 


HISTORY. 

Freeman    (Edward    A.) — OLD -ENGLISH  HISTORY. 

By  EDWARD  A.  FREEMAN,  D.C.L.,  late  Fellow  of  Trinity 
College,  Oxford.  With  Five  Coloured  Maps.  Fourth  Edition. 
Extra  fcap.  8vo.  half-bound.  6s. 

"I  have,  I  hope"  the  author  says,  "shown  that  it  is  perfectly  easy  to 
teach  children,  from  the  very  first,  to  distinguish  true  history  alike  from 
legend  and  from  wilful  invention,  and  also  to  understand  the  nature  of 
historical  authorities  and  to  weigh  one  statement  against  another.  I  have 
throughout  striven  to  connect  the  history  of  England  with  the  general 
history  of  civilized  Europe,  and  I  have  especially  tried  to  make  the 
book  serve  as  an  incentive  to  a  more  accurate  study  of  historical 
geography."  In  the  present  edition  the  whole  has  hen  carefully  revised, 


26  EDUCATIONAL  BOOKS. 

and  such  improvements  as  suggested  themselves  have  been  introduced. 
* '  The  book  indeed  is  full  of  instruction  and  interest  to  students  of  all 
ages,  and  he  must  be  a  well-informed  man  indeed  who  will  not  rise  'from 
its  perusal  with  clearer  and  more  accurate  ideas  of  a  too  much  neglected 
portion  of  English  History." — SPECTATOR. 

Green. — A  SHORT  HISTORY  OF  THE  ENGLISH  PEOPLE. 

By  JOHN  RICHARD  GREEN.     With  Coloured  Maps,  Genealogical 
Tables,    and    Chronological    Annals.        Crown   8vo.         &s.   6d. 
Thirty-fourth  Thousand. 
"  Stands  alone  as  the  one  general  history  of  the  country,  for  the  sake  of 

which  all  others,  if  young  and  old  are  wise,  will  be  speedily  and  surely  set 

aside. " — ACADEMY. 

Historical   Course   for   Schools. — Edited   by   EDWARD 

A.  FREEMAN,  D.C.L.,  late  Fellow  of  Trinity  College,  Oxford. 
The  object  of  the  present  series  is  to  put  forth  clear  and  correct  views 
of  history  in  simple  language,  and  in  the  smallest  space  and  cheapest 
form  in  which  it  could  be  done.  It  is  meant  in  the  first  place  for 
Schools  ;  but  it  is  often  found  that  a  book  for  schools  proves  useful 
for  other  readers  as  well,  and  it  is  hoped  that  this  may  be  the  case 
with  the  little  books  the  first  instalment  of  which  is  now  given  to 
the  world. 

I.  GENERAL    SKETCH    OF    EUROPEAN     HISTORY.      By 
EDWARD  A.  FREEMAN,  D.C.L.     Fourth  Edition.     i8mo.  cloth. 
3J.  &£ 

"//  supplies  the  great  want  of  a  good  foundation  for  historical  teach- 
ing. The  scheme  is  an  excellent  one,  and  this  instalment  has  been 
executed  in  a  way  that  promises  much  for  the  volumes  that  are  yet  to 
appear." — EDUCATIONAL  TIMES. 

II.  HISTORY   OF  ENGLAND.     By  EDITH  THOMPSON.      Fifth 
Edition.     i8mo.     2s.  6d. 

"  Freedom  from  prejudice,  simplicity  of  style,  and  accuracy  of  statement, 
are  the  characteristics  of  this  little  volume.  It  is  a  trustworthy  text- book 
and  likely  to  be  generally  serviceable,  in  schools." — PALL  MALL  GAZETTE. 
"  Upon  the  whole,  this  manual  is  the  best  sketch  oj  English  history  for  the 
use  oj  young  people  we  have  yet  met  with." — ATHEN^UM. 

III.  HISTORY  OF  SCOTLAND.     By  MARGARET  MACARTHUR. 
i8mo.     2s. 

"An  excellent  summary,  unimpeachable  as  to  facts,  and  putting  them  in 
the  clearest  and  most  impartial  light  attainable" — GUARDIAN.  "  Miss 
Macarthur  has  performed  her  task  with  admirable  care,  clearness,  and 
fulness,  and  we  have  now  for  the  first  time  a  really  good  School  History 
of  Scotland." — EDUCATIONAL  TIMES. 

IV.  HISTORY  OF  ITALY.    By  the  Rev.  W.  HUNT,  M.A.     i8mo. 

3f- 

"  It  possesses  the  same  solid  merit  as  its  predecessors  ....  the  same 
scrupulous  care  about  fidelity  in  details.  .  .  .  It  is  distinguished,  too,  by 


HISTORY.  27 


Historical  Course  for  Schools — continued. 

information  on  art,  architecture,  and  social  politics,  in  which  the  writers 
grasp  is  seen  by  the  firmness  and  clearness  of  his  touch." — EDUCATIONAL 
TIMES. 

V.  HISTORY  OF   GERMANY.     By  J.  SIME,  M.A.     iSmo.     3*. 
"  A  remarkably  clear  and  impressive  History  of  Germany.     Its  great 

events  are  wisely  kept  as  central  figures,  and  the  smaller  events  are  carefully 
kept,  not  only  subordinate  and  subservient,  but  most  skilfully  woven  into 
the  texture  of  the  historical  tapestry  presented  to  the  eye. " — STANDARD. 

VI.  HISTORY  OF  AMERICA.    By  JOHN  A.  DOYLE.    With  Maps. 
i8mo.     4s.  6d. 

"  Mr.  Doyle  has  performed  his  task  with  admirable  care,  fulness,  and 
charness,  and  for  the  first  time  we  have  for  schools  an  accurate  and  inter- 
esting history  of  America,  from  the    earliest   to   the  present  time." — 
STANDARD. 
The  following  will  shortly  be  issued : — 

FRANCE.    By  CHARLOTTE  M.  YONGE. 
GREECE.    By  J.  ANNAN  BRYCE,  B.A. 

History  Primers. — Edited  by  JOHN  RICHARD  GREEN.  Author 

of  "A  Short  History  of  the  English  People.'' 
ROME.     By  the  Rev.   M.    Creighton,   M.A.,   Fellow  and  Tutor  of 

Merton  College,  Oxford.     With  Eleven  Maps.     i8mo.     u. 
"  The  Author  has  been   curiously  successful  in  idling  in  an  intelli- 
gent way  the  story  of  Rome  from  first  to  last." — SCHOOL    BOARD 
CHRONICLE. 

GREECE.     By  C.  A.  Fyffe,   M.A.,  Fellow  and  late  Tutor  of  Uni- 
versity College,  Oxford.     With  Five  Maps.     i8mo.     is. 
"  We  give  our   unqualified  praise  to  this  little  manual" — SCHOOL- 
MASTER. 

In  preparation : — 

EUROPE.     By  E.  A.  FREEMAN,  D.C.L.,  LL.D. 
ENGLAND.    By  J.  R.  GREEN,  M.A. 
FRANCE.    By  CHARLOTTE  M.  YONGE. 
GEOGRAPHY.     By  GEORGE  GROVE,  D.C.L. 

Michelet.— A  SUMMARY  OF  MODERN  HISTORY.     Trans- 
lated  from  the  French  of  M.  Michelet,  and  continued  to  the  Present 
Time,  by  M.  C.  M.  Simpson.     Globe  8vo.     ^.  6d. 
"  We  are  glad  to  see  one  of  the  ablest  and  most  useful  summaries  of 
European  history  put  into  the  hands  of  English  readers.     The  trans- 
lation is  excellent" — STANDARD. 
Yonge   (Charlotte    M.}— A  PARALLEL  HISTORY  OF 

FRANCE  AND  ENGLAND  :  consisting  of  Outlines  and  Dates. 
By  CHARLOTTE  M.  YONGE,  Author  of  "The  Heir  of  Redclyffe, 
"  Cameos  of  English  History,"  &c.  &c.      Oblong  4to.     3*.  bd. 
"  We  can  imagine  few  more  really  advantageous  courses  of  historical 
study  for  a  young  mind  than  going  carefully  and  steadily  through  Mtss 
Yonge' s  excellent  little  book.  "—EDUCATIONAL  TIMES, 


28  EDUCATIONAL  BOOKS. 

Yonge  (Charlotte  M.) — continued. 

CAMEOS  FROM  ENGLISH  HISTORY.     From  Rollo  to  Edward 
II.     By  the  Author  of  "The  Heir  of  Redclyffe."    Extra  fcap. 
8vo.     Third  Edition,  enlarged.     $s. 
A  hook  for  young  people  just  bevond  the  elementary  histories  of  England, 

and  able  to  enter  in  some  degree  into  the  real  spirit  of  events,  and  to  be 

struck  with  characters  and  scenes  presented  in  some  relief.     "  Instead  of 

dry  details,  we   have  living  pictures,  faithful,  vivid,  and  striking." — 

NONCONFORMIST. 

A  SECOND  SERIES  OF  CAMEOS  FROM  ENGLISH  HISTORY. 

THE  WARS  IN  FRANCE.     Third  Edition.     Extra  fcap.  8vo.     5-r. 
"  Though  mainly  intended  for  young  readers,  they  will,  if  we  mistake 

not,   be  found  very  acceptable  to  those  of  more  mature  years,  and  the 

life  and  reality  imparted  to  the  dry  bones  of  history  cannot  fail  to  be 

attractive  to  readers  of  every  age"— JOHN  BULL. 

EUROPEAN  HISTORY.  Narrated  in  a  Series  of  Historical  Selec- 
tions from  the  Best  Authorities.  Edited  and  arranged  by  E.  M. 
SEWELL  and  C.  M.  YONGE.  First  Series,  1003 — 1154.  Third 
Edition.  Crown  8vo.  6s.  Second  Series,  1088—1228.  Crown 
8vo.  6s.  Third  Edition. 
"  We  know  of  scarcely  anything  which  is  so  likely  to  raise  to  a  higher 

level  the  average  standard  of  English  education." — GUARDIAN. 


DIVINITY. 

%*  For  other  Works  by  these  Authors,  see  THEOLOGICAL  CATALOGUE. 
Abbott    (Rev.    E.    A.) — BIBLE     LESSONS.     By  the  Rev. 

E.  A.  ABBOTT,  M.A.,  Head  Master  of  the  City  of  London  School. 

Second  Edition.     Crown  8vo.     4^.  6d. 

"  Wise,  suggestive,  and  really  profound  initiation  into  religious  thought." 
— GUARDIAN.  "  I  think  nobody  could  read  them  without  being  both  the 
better  for  them  himself,  and  being  also  able  to  see  how  this  difficult  duty  of 
imparting  a  sound  religious  education  may  be  effected" — BISHOP  OF  ST. 
DAVID'S  AT  ABERGWILLY. 

Arnold.— A   BIBLE-READING    FOR    SCHOOLS.     The 

GREAT  PROPHECY  OF  ISRAEL'S  RESTORATION  (Isaiah,  Chapters 
40 — 66).  Arranged  and  Edited  for  Young  Learners.  By  MAT- 
THEW ARNOLD,  D.C.L.,  formerly  Professor  of  Poetry  in  the 
University  of  Oxford,  and  Fellow  of  Oriel.  Fourth  Edition.  i8mo. 
cloth,  is. 

"  There  can  be  no  doubt  that  it  will  be  found  excellently  calculated  to 
further  instruction  in  Biblical  literature  in  any  school  into  which  it  may 
be  introduced ;  and  we  can  safely  sav  thai  whatever  school  uses  the  book, 
it  zvilt  enable  its  ptipils  to  unaersiand  Isaiah,  a  great  advantage  corn-bared 
with  ether  establishments  which  do  not  avail  themselves  of  it" — TIMES. 


DIVINITY.  2g 


Arnold.— ISAIAH  XL.-LXVI.  With  the  Shorter  Prophecies 
allied  to  it.  Arranged  and  Edited  with  Notes  by  MATTHEW 
ARNOLD.  Crown  8vo.  5-r. 

Golden  Treasury  Psalter.— Students'  Edition.  Being  an 
Edition  of  "The  Psalms  Chronologically  Arranged,  by  Four 
Friends,"  with  briefer  Notes.  i8mo.  3^.  6d, 

Hardwick.— A  HISTORY  OF  THE  CHRISTIAN  CHURCH. 

Middle  Age.  From  Gregory  the  Great  to  the  Excommunication 
of  Luther.  Edited  by  WILLIAM  STUBBS,  M.A.,  Regius  Professor 
of  Modern  History  in  the  University  of  Oxford.  With  Four  Maps 
constructed  for  this  work  by  A,  KEITH  JOHNSTON.  Fourth  Edition. 
Crown  8vo.  iQs.  6d. 

For  this  edition  Professor  Stubbs  has  carefully  revised  both  text  and 
notes,  making  stick  corrections  of  facts,  dates,  and  the  like  as  the  results 
of  recent  research  warrant.  The  doctrinal,  historical,  and  generally 
speculative  views  of  the  late  author  have  been  preserved  intact.  "As  a 
manual  for  the  student  of  ecclesiastical  history  in  the  Middle  Ages,  we 
know  no  English  work  which  can  be  compared  to  Mr.  Hardwick 's 
book. » — GUARDIAN. 

A  HISTORY  OF  THE  CHRISTIAN  CHURCH  DURING  THE 
REFORMATION.  By  ARCHDEACON  HARDWICK.  Fourth 
Edition.  Edited  by  Professor  STUBBS.  Crown  8vo.  los.  6d. 

Maclear. — Works  by  the  Rev.  G.  F.  MACLEAR,  D.D.,  Head 
Master  of  King's  College  School. 

A  CLASS-BOOK  OF  OLD   TESTAMENT  HISTORY.      Eighth 

Edition,  with  Four  Maps.     i8mo.  cloth.     4^.  6d. 
"A  careful  and  elaborate  though  brief  compendium  oj  all  that  modern 
research  has  done  for  the  illustration  of  the  Old  Testament.     We  know 
of  no  work  which  contains  so  much  important  information  in  so  small 
a  compass" — BRITISH  QUARTERLY  REVIEW. 

A  CLASS-BOOK  OF  NEW  TESTAMENT  HISTORY,  including 
the  Connexion  of  the  Old  and  New  Testament.     With  Four  Maps. 
Fifth  Edition.     i8mo.  cloth.     5*.  6d. 
"A  singularly  clear  and  orderly  arrangement  of  the  Sacred  Story. 

His  work  is  solidly  and  completely  done." — ATHENAEUM. 

A   SHILLING  BOOK    OF    OLD    TESTAMENT    HISTORY, 

for   National  and   Elementary    Schools.       With   Map.       i8mo. 

cloth.     New  Edition. 
A   SHILLING    BOOK   OF    NEW    TESTAMENT    HISTORY, 

for    National    and  Elementary  Schools.       With  Map.       i8mo. 

cloth.     New  Edition. 

'    These  works  have  been  carefully  abridged  from  the  authors  larger 
manuals. 


3o  EDUCATIONAL  BOOKS. 

Maclear — continued. 

CLASS-BOOK  OF  THE  CATECHISM  OF  THE  CHURCH  OF 
ENGLAND.    New  and  Cheaper  Edition.     i8mo.  cloth,     is.  6d. 
lt  It  is  indeed  the  work  of  a  scholar  and  divine,  and  as  such,  though 
extremely  simple,  it  is  also  extremely  instructive.     There  are  few  clergy- 
men who   would  not  find  it  useful  in  preparing  candidates  for  Confir- 
mation ;  and  there  are  not  a  few  who  would  find  it  useful  to  themselves 
as  well" — LITERARY  CHURCHMAN. 

A  FIRST  CLASS-BOOK  OF  THE  CATECHISM  OF  THE 
CHURCH  OF  ENGLAND,  with  Scripture  Proofs,  for  Junior 
Classes  and  Schools.  i8mo.  6d.  New  Edition. 
A  MANUAL  OF  INSTRUCTION  FOR  CONFIRMATION  AND 
FIRST  COMMUNION.  With  Prayers  and  Devotions.  Royal 
32mo.  cloth  extra,  red  edges.  2s. 

"  It  is  earnest,  orthodox,  and  affectionate  in  tone.      The  form  of  self- 
examination  is  particularly  good." — JOHN  BULL. 

THE  ORDER  OF  CONFIRMATION,  WITH  PRAYERS  AND 
DEVOTIONS.  32mo.  6d. 

FIRST  COMMUNION,  WITH  PRAYERS  AND  DEVOTIONS 
FOR  THE  NEWLY  CONFIRMED.  32mo.  6d. 

Maurice.— THE  LORD'S  PRAYER,  THE  CREED,  AND 
THE  COMMANDMENTS.  A  Manual  for  Parents  and  School- 
masters.  To  which  is  added  the  Order  of  the  Scriptures.  By  the 
Rev.  F.  DENISON  MAURICE,  M.A.  i8mo.  cloth  limp.  u. 

Procter. — A  HISTORY  OF  THE   BOOK  OF  COMMON 

PRAYER,  with  a  Rationale  of  its  Offices.  By  P^RANCIS  PROCTER, 
M.A.  Twelfth  Edition,  revised  and  enlarged.  Crown  8vo. 
lew.  6d. 

Procter    and    Maclear.— AN   ELEMENTARY   INTRO- 

DUCTION  TO  THE  BOOK  OF  COMMON  PRAYER. 
Re-arranged  and  supplemented  by  an  Explanation  of  the  Morning 
and  Evening  Prayer  and  the  Litany.  By  the  Rev.  F.  PROCTER 
and  the  Rev.  G.  F.  MACLEAR.  New  Edition.  i8mo.  2s.  6d. 

Psalms  of  David  Chronologically  Arranged.     By 

Four    Friends.       An   Amended    Version,    with    Historical 
Introduction    and    Explanatory   Notes.       Second,  and    Cheaper 
Edition,  with  Additions  and  Corrections.     Crown  8vo.     8s.  6d. 
"  One  of  the  most  instructive  and  valuable  books  that  has  been  published 
for  many  years." — SPECTATOR. 

Ramsay. — THE  CATECHISER'S  MANUAL;  or,  the  Church 
Catechism  Illustrated  and  Explained,  for  the  use  of  Clergymen, 
Schoolmasters,  and  Teachers.  By  the  Rev.  ARTHUR  RAMSAY, 
M.A.  Second  Edition.  i8mo.  is.  6d. 


DIVINITY.  3I 


Simpson.— AN  EPITOME  OF  THE  HISTORY  OF  THE 
CHRISTIAN  CHURCH.  By  WILLIAM  SIMPSON,  M.A. 
Fifth  Edition.  Fcap.  8vo.  3*.  6d. 

Swainson.—  A  HANDBOOK  to  BUTLER'S  ANALOGY.    By 

C.   A.    SWAINSON,  D.D.,    Canon  of  Chichester.     Crown   8vo. 
is.  $d, 

Trench — SYNONYMS  OF  THE  NEW  TESTAMENT.    By 

R.    CHENEVIX  TRENCH,    D.D.,    Archbishop  of  Dublin.     New 

Edition,  enlarged.     8vo.  cloth.     12s. 
WestCOtt.— Works   by  BROOKE  FOSS    WESTCOTT,  B.D., 

Canon  of  Peterborough. 
A     GENERAL     SURVEY     OF     THE    HISTORY     OF    THE 

CANON    OF  THE    NEW    TESTAMENT    DURING   THE 

FIRST  FOUR  CENTURIES.     Fourth  Edition.     With  Preface 

on  "  Supernatural  Religion."     Crown  8vo.      los.  6d. 
"  Theological  students,  and  not  they  only,  but  the  general  public,  owe  a 
deep   debt  of  gratitude  to  Mr.    Westcott  for   bringing  this  subject  fairly 
before  them  in  this  candid  and  comprehensive  essay As  a  theo- 
logical, work  it  is  at  once  perfectly  Jair  and  impartial,  and  imbued  with 
a  thoroughly  religious  spirit;    and  as  a  manual  it  exhibits,  in  a  lucid 
form  and  in  a  narrow  compass,  the  results  of  extensive  research  and 
accurate  thought.     We  cordially  recommend  it. " — SATURDAY  REVIEW. 
INTRODUCTION  TO  THE  STUDY  OF  THE  FOUR  GOSPELS. 

Fifth  Edition.     Crown  8vo.     lew.  6d. 

"  To  learning  and  accuracy  which  commands  respect  and  confidence, 
he  unites  what  are  not  always  to  be  found  in  union  with  these  qualities,  the 
no  less  valuable  faculties  of  lucid  arrangement  and  graceful and  facile  ex- 
pression."— LONDON  QUARTERLY  REVIEW. 
THE   BIBLE   IN   THE   CHURCH.      A   Popular  Account  of  the 

Collection  and  Reception  of  the  Holy  Scriptures  in  the  Christian 

Churches.     New  Edition.     i8mo.  cloth.     4^.  6d. 

'*  We  would  recommend  every  one  who  loves  and  studies  the  Bible  to  read 

and  ponder    this   exquisite  little  book.      Mr.    Westcotfs  account  of  the 

'  Canon*  is  true  history  in  its  highest  sense" — LITERARY  CHURCHMAN. 

THE  GOSPEL   OF   THE   RESURRECTION.      Thoughts  on   its 

Relation  to    Reason   and  History.     New   Edition.     Crown   8vo. 

6s. 

WilSOn. — THE  BIBLE  STUDENT'S  GUIDE  to  the  more  Correct 
Understanding  of  the  English  translation  of  the  Old  Testament, 
by  reference  to  the  Original  Hebrew.  By  WILLIAM  WILSON, 
D,D.,  Canon  of  Winchester,  late  Fellow  of  Queen's  College, 
Oxford.  Second  Edition,  carefully  Revised.  4to.  cloth.  25 j. 
"  For  all  earnest  students  of  the  Old  Testammt  Scriptures  it  is  a 

most  valuable  Manual.      Its  arrangement  is  so  simple  that  those  who 

possess  only  their   mother-tongue,  if  they  will  take  a  little  pains,   may 

employ  it  with  great  profit. " — NONCONFORMIST. 


32  EDUCATIONAL  BOOKS. 

Yonge  (Charlotte   M.)— SCRIPTURE  READINGS  FOR 

SCHOOLS  AND  FAMILIES.       By  CHARLOTTE  M.  YONGE, 
Author  of  "The  Heir  of  Redclyffe."     FIRST   SERIES.    Genesis 
to  Deuteronomy.    Globe  8vo. .  is.  6d.    With  Comments.    Second 
Edition.     $s.  6d. 
SECOND   SERIES.     From  JOSHUA   to    SOLOMON.     Extra  fcap. 

8vo.     is.  6d.     With  Comments,  $s.  6d. 
THIRD  SERIES.     The  KINGS  and  the  PROPHETS.     Extra  fcap. 

8vo.     is.  6d.     With  Comments,  $s.  6d. 

Actual  need  has  led  the  author  to  endeavour  to  prepare  a  reading  book  con  - 
venient  for  study  with  children,  containing  the  very  words  of  the  Bible,  with 
only  a  few  expedient  omissions,  and  arranged  in  Lessons  of  such  length  as  by 
experience  she  has  found  to  suit  with  children's  ordinary  power  of  accurate 
attentive  interest.  The  verse  form  has  been  retained,  because  of  its  con- 
venience for  children  reading  in  class,  and  as  more  resembling  their  Bibles  ; 
but  the  poetical  portions  have  been  given  in  their  lines.  When  Psalms  or 
portions  from  the  Prophets  illustrate  or  fall  in  with  the  narrative  they  are 
given  in  their  chronological  sequence.  The  Scripture  portion,  with  a  very 
few  notes  explanatory  of  mere  words,  is  bound  up  apart,  to  be  used  by 
children,  while  the  same  is  also  supplied  with  a  brief  comment,  the  purpose 
of  which  is  either  to  assist  the  teacher  in  explaining  the  lesson,  or  to  be 
used  by  more  advanced  young  people  to  whom  it  may  not  be  possible  to  give 
access  to  the  authorities  whence  it  has  been  taken.  Professor  Huxley,  at  a 
meeting  of  the  London  School  Board,  particularly  mentioned  the  selection 
made  by  Miss  Yonge  as  an  example  of  how  selections  might  be  made  from 
the  Bible  for  School  Reading.  See  TIMES,  March  30,  1871. 


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